From 171bae1f5c13144f1574db11ac9a19732ec567cc Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Sun, 25 Mar 2018 17:34:29 -0400
Subject: [PATCH 01/20] GUACAMOLE-527: Add basic check for known hosts file for
 SSH connections.

---
 src/common-ssh/ssh.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 5ea6feab..5099de25 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -35,6 +35,7 @@
 #include <netdb.h>
 #include <netinet/in.h>
 #include <pthread.h>
+#include <pwd.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
@@ -509,6 +510,47 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         return NULL;
     }
 
+    /* Check known_hosts */
+    size_t len;
+    int type;
+    struct passwd *pw = getpwuid(getuid());
+    char *homedir = pw->pw_dir;
+    char *known_hosts = strcat(homedir, "/.ssh/known_hosts");
+    LIBSSH2_KNOWNHOSTS *ssh_known_hosts = libssh2_knownhost_init(session);
+
+    libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+    const char *fingerprint = libssh2_session_hostkey(session, &len, &type);
+
+    if (fingerprint) {
+        struct libssh2_knownhost *host;
+        int check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
+                                            fingerprint, len,
+                                            LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                            LIBSSH2_KNOWNHOST_KEYENC_RAW,
+                                            &host);
+
+        switch (check) {
+            case LIBSSH2_KNOWNHOST_CHECK_MATCH:
+                guac_client_log(client, GUAC_LOG_DEBUG,
+                    "Host key match found.");
+                break;
+            case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Host key not found in known hosts file.");
+                break;
+            case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Host key does not match host entry.");
+                break;
+            case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
+            default:
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Host could not be checked against known hosts.");
+        }
+
+
+    }
+
     /* Perform handshake */
     if (libssh2_session_handshake(session, fd)) {
         guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,

From 0d82cd1e6c78606a6b4d65b6d2441b02479fda88 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Thu, 5 Apr 2018 07:36:37 -0400
Subject: [PATCH 02/20] GUACAMOLE-527: Add host key and type settings.

---
 src/common-ssh/common-ssh/ssh.h |  3 +-
 src/common-ssh/ssh.c            | 85 +++++++++++++++++++++------------
 src/protocols/ssh/settings.c    | 22 +++++++++
 src/protocols/ssh/settings.h    | 10 ++++
 4 files changed, 89 insertions(+), 31 deletions(-)

diff --git a/src/common-ssh/common-ssh/ssh.h b/src/common-ssh/common-ssh/ssh.h
index 8026549d..e25b6263 100644
--- a/src/common-ssh/common-ssh/ssh.h
+++ b/src/common-ssh/common-ssh/ssh.h
@@ -98,7 +98,8 @@ void guac_common_ssh_uninit();
  *     if the connection or authentication were not successful.
  */
 guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
-        const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive);
+        const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive,
+        const char* host_key_type, const char* host_key);
 
 /**
  * Disconnects and destroys the given SSH session, freeing all associated
diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 5099de25..a1a62f60 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -415,7 +415,8 @@ static int guac_common_ssh_authenticate(guac_common_ssh_session* common_session)
 }
 
 guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
-        const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive) {
+        const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive,
+        const char* host_key_type, const char* host_key) {
 
     int retval;
 
@@ -511,44 +512,68 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     }
 
     /* Check known_hosts */
-    size_t len;
-    int type;
+    /* Get known hosts file from user running guacd */
     struct passwd *pw = getpwuid(getuid());
     char *homedir = pw->pw_dir;
     char *known_hosts = strcat(homedir, "/.ssh/known_hosts");
     LIBSSH2_KNOWNHOSTS *ssh_known_hosts = libssh2_knownhost_init(session);
-
     libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
-    const char *fingerprint = libssh2_session_hostkey(session, &len, &type);
 
-    if (fingerprint) {
-        struct libssh2_knownhost *host;
-        int check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
-                                            fingerprint, len,
-                                            LIBSSH2_KNOWNHOST_TYPE_PLAIN|
-                                            LIBSSH2_KNOWNHOST_KEYENC_RAW,
-                                            &host);
+    /* Add host key provided from settings */
+    if (strcmp(host_key, "") > 0) {
 
-        switch (check) {
-            case LIBSSH2_KNOWNHOST_CHECK_MATCH:
-                guac_client_log(client, GUAC_LOG_DEBUG,
-                    "Host key match found.");
-                break;
-            case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
-                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Host key not found in known hosts file.");
-                break;
-            case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
-                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Host key does not match host entry.");
-                break;
-            case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
-            default:
-                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Host could not be checked against known hosts.");
-        }
+        int kh_key_type = 0;
+        if (strcmp(host_key_type, "ssh-rsa") == 0)
+            kh_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
+        else if(strcmp(host_key_type, "ssh-dss") == 0)
+            kh_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
+        else if(strcmp(host_key_type, "rsa1") == 0)
+            kh_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
+        else
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Invalid SSH host key type %s", host_key_type);
 
+        if (libssh2_knownhost_addc(ssh_known_hosts, hostname, NULL, host_key, strlen(host_key),
+                NULL, 0, LIBSSH2_KNOWNHOST_TYPE_PLAIN|LIBSSH2_KNOWNHOST_KEYENC_BASE64|
+                         kh_key_type, NULL))
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Failed to add host key to known hosts store for %s", hostname);
+    }
 
+    /* Get fingerprint of host we're connecting to */
+    size_t fp_len;
+    int fp_type;
+    const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
+
+    if (!fingerprint || strcmp(fingerprint, "") == 0) {
+        guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Could not retrieve fingerprint of SSH server %s", hostname);
+    }
+
+    struct libssh2_knownhost *host;
+    int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
+                                         fingerprint, fp_len,
+                                         LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                         LIBSSH2_KNOWNHOST_KEYENC_RAW,
+                                         &host);
+
+    switch (kh_check) {
+        case LIBSSH2_KNOWNHOST_CHECK_MATCH:
+            guac_client_log(client, GUAC_LOG_DEBUG,
+                "Host key match found.");
+            break;
+        case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Host key not found in known hosts file.");
+            break;
+        case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Host key does not match host entry.");
+            break;
+        case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
+        default:
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Host could not be checked against known hosts.");
     }
 
     /* Perform handshake */
diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index 2ce97903..bc650e99 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -31,6 +31,8 @@
 /* Client plugin arguments */
 const char* GUAC_SSH_CLIENT_ARGS[] = {
     "hostname",
+    "host_key_type",
+    "host_key",
     "port",
     "username",
     "password",
@@ -68,6 +70,16 @@ enum SSH_ARGS_IDX {
      */
     IDX_HOSTNAME,
 
+    /**
+     * The type of public SSH host key provided.  Optional.
+     */
+    IDX_HOST_KEY_TYPE,
+
+    /**
+     * The Base64-encoded public SSH host key.  Optional.
+     */
+    IDX_HOST_KEY,
+
     /**
      * The port to connect to. Optional.
      */
@@ -247,6 +259,14 @@ guac_ssh_settings* guac_ssh_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_HOSTNAME, "");
 
+    settings->host_key_type =
+        guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
+                IDX_HOST_KEY_TYPE, "ssh-rsa");
+
+    settings->host_key =
+        guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
+                IDX_HOST_KEY, NULL);
+
     settings->username =
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_USERNAME, NULL);
@@ -384,6 +404,8 @@ void guac_ssh_settings_free(guac_ssh_settings* settings) {
 
     /* Free network connection information */
     free(settings->hostname);
+    free(settings->host_key_type);
+    free(settings->host_key);
     free(settings->port);
 
     /* Free credentials */
diff --git a/src/protocols/ssh/settings.h b/src/protocols/ssh/settings.h
index 393cfc0c..ac8400ec 100644
--- a/src/protocols/ssh/settings.h
+++ b/src/protocols/ssh/settings.h
@@ -70,6 +70,16 @@ typedef struct guac_ssh_settings {
      */
     char* hostname;
 
+    /**
+     * The type of public SSH host key.
+     */
+    char* host_key_type;
+
+    /**
+     * The public SSH host key.
+     */
+    char* host_key;
+
     /**
      * The port of the SSH server to connect to.
      */

From 9112c4f32f719ca1b4ae5f301e36f96c6190ba9d Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Thu, 5 Apr 2018 08:52:16 -0400
Subject: [PATCH 03/20] GUACAMOLE-527: Enable host key setting for SFTP
 connections.

---
 src/common-ssh/common-ssh/ssh.h  |  2 +-
 src/common-ssh/ssh.c             | 16 ++-----------
 src/protocols/rdp/rdp.c          |  3 ++-
 src/protocols/rdp/rdp_settings.c | 40 ++++++++++++++++++++++++++++++++
 src/protocols/rdp/rdp_settings.h | 10 ++++++++
 src/protocols/ssh/settings.c     | 23 +++++++++++++-----
 src/protocols/ssh/settings.h     |  2 +-
 src/protocols/ssh/ssh.c          |  6 +++--
 src/protocols/vnc/settings.c     | 37 +++++++++++++++++++++++++++++
 src/protocols/vnc/settings.h     | 10 ++++++++
 src/protocols/vnc/vnc.c          |  3 ++-
 11 files changed, 126 insertions(+), 26 deletions(-)

diff --git a/src/common-ssh/common-ssh/ssh.h b/src/common-ssh/common-ssh/ssh.h
index e25b6263..8f6f6893 100644
--- a/src/common-ssh/common-ssh/ssh.h
+++ b/src/common-ssh/common-ssh/ssh.h
@@ -99,7 +99,7 @@ void guac_common_ssh_uninit();
  */
 guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive,
-        const char* host_key_type, const char* host_key);
+        const int host_key_type, const char* host_key);
 
 /**
  * Disconnects and destroys the given SSH session, freeing all associated
diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index a1a62f60..0eb9fa10 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -416,7 +416,7 @@ static int guac_common_ssh_authenticate(guac_common_ssh_session* common_session)
 
 guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive,
-        const char* host_key_type, const char* host_key) {
+        const int host_key_type, const char* host_key) {
 
     int retval;
 
@@ -522,20 +522,9 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     /* Add host key provided from settings */
     if (strcmp(host_key, "") > 0) {
 
-        int kh_key_type = 0;
-        if (strcmp(host_key_type, "ssh-rsa") == 0)
-            kh_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
-        else if(strcmp(host_key_type, "ssh-dss") == 0)
-            kh_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
-        else if(strcmp(host_key_type, "rsa1") == 0)
-            kh_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
-        else
-            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Invalid SSH host key type %s", host_key_type);
-
         if (libssh2_knownhost_addc(ssh_known_hosts, hostname, NULL, host_key, strlen(host_key),
                 NULL, 0, LIBSSH2_KNOWNHOST_TYPE_PLAIN|LIBSSH2_KNOWNHOST_KEYENC_BASE64|
-                         kh_key_type, NULL))
+                         host_key_type, NULL))
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
                 "Failed to add host key to known hosts store for %s", hostname);
     }
@@ -627,4 +616,3 @@ void guac_common_ssh_destroy_session(guac_common_ssh_session* session) {
     free(session);
 
 }
-
diff --git a/src/protocols/rdp/rdp.c b/src/protocols/rdp/rdp.c
index 45082bb0..30b19326 100644
--- a/src/protocols/rdp/rdp.c
+++ b/src/protocols/rdp/rdp.c
@@ -974,7 +974,8 @@ void* guac_rdp_client_thread(void* data) {
         /* Attempt SSH connection */
         rdp_client->sftp_session =
             guac_common_ssh_create_session(client, settings->sftp_hostname,
-                    settings->sftp_port, rdp_client->sftp_user, settings->sftp_server_alive_interval);
+                    settings->sftp_port, rdp_client->sftp_user, settings->sftp_server_alive_interval,
+                    settings->sftp_host_key_type, settings->sftp_host_key);
 
         /* Fail if SSH connection does not succeed */
         if (rdp_client->sftp_session == NULL) {
diff --git a/src/protocols/rdp/rdp_settings.c b/src/protocols/rdp/rdp_settings.c
index 35f7f202..78afe374 100644
--- a/src/protocols/rdp/rdp_settings.c
+++ b/src/protocols/rdp/rdp_settings.c
@@ -35,6 +35,9 @@
 #include "compat/winpr-wtypes.h"
 #endif
 
+#ifdef ENABLE_COMMON_SSH
+#include <libssh2.h>
+#endif
 #include <stddef.h>
 #include <string.h>
 
@@ -81,6 +84,8 @@ const char* GUAC_RDP_CLIENT_ARGS[] = {
 #ifdef ENABLE_COMMON_SSH
     "enable-sftp",
     "sftp-hostname",
+    "sftp-host-key-type",
+    "sftp-host-key",
     "sftp-port",
     "sftp-username",
     "sftp-password",
@@ -355,6 +360,17 @@ enum RDP_ARGS_IDX {
      */
     IDX_SFTP_HOSTNAME,
 
+    /**
+     * The type of public SSH host key provided.  If not specified, it defaults
+     * to SSH-RSA.
+     */
+    IDX_SFTP_HOST_KEY_TYPE,
+
+    /**
+     * The public SSH host key of the SFTP server.  Optional.
+     */
+    IDX_SFTP_HOST_KEY,
+
     /**
      * The port of the SSH server to connect to for SFTP. If blank, the default
      * SSH port of "22" will be used.
@@ -822,6 +838,30 @@ guac_rdp_settings* guac_rdp_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
                 IDX_SFTP_HOSTNAME, settings->hostname);
 
+    /* The public SSH host key. */
+    settings->sftp_host_key =
+        guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
+                IDX_SFTP_HOST_KEY, NULL);
+
+    if(settings->sftp_host_key) {
+        /* Type of public SSH host key. */
+        char* str_host_key_type = guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
+                    IDX_SFTP_HOST_KEY_TYPE, "ssh-rsa");
+        
+        if (strcmp(str_host_key_type, "ssh-rsa") == 0)
+            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
+        else if (strcmp(str_host_key_type, "ssh-dss") == 0)
+            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
+        else if (strcmp(str_host_key_type, "rsa1") == 0)
+            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
+        else {
+            guac_user_log(user, GUAC_LOG_WARNING, "Invalid host key type specified %s.  "
+                    "Ignoring host key.", str_host_key_type);
+            settings->sftp_host_key = NULL;
+        }
+
+    }
+
     /* Port for SFTP connection */
     settings->sftp_port =
         guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
diff --git a/src/protocols/rdp/rdp_settings.h b/src/protocols/rdp/rdp_settings.h
index ad71ca06..0a442799 100644
--- a/src/protocols/rdp/rdp_settings.h
+++ b/src/protocols/rdp/rdp_settings.h
@@ -342,6 +342,16 @@ typedef struct guac_rdp_settings {
      */
     char* sftp_hostname;
 
+    /**
+     * The type of the public SSH hos key.
+     */
+    int sftp_host_key_type;
+
+    /**
+     * The public SSH host key.
+     */
+    char* sftp_host_key;
+
     /**
      * The port of the SSH server to connect to for SFTP.
      */
diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index bc650e99..4653e96f 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -24,6 +24,7 @@
 
 #include <guacamole/user.h>
 
+#include <libssh2.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
@@ -259,14 +260,26 @@ guac_ssh_settings* guac_ssh_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_HOSTNAME, "");
 
-    settings->host_key_type =
-        guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
-                IDX_HOST_KEY_TYPE, "ssh-rsa");
-
     settings->host_key =
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_HOST_KEY, NULL);
 
+    if (settings->host_key) {
+        char* str_host_key_type = guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
+                    IDX_HOST_KEY_TYPE, "ssh-rsa");
+        if (strcmp(str_host_key_type, "ssh-rsa") == 0)
+            settings->host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
+        else if (strcmp(str_host_key_type, "ssh-dss") == 0)
+            settings->host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
+        else if (strcmp(str_host_key_type, "rsa1") == 0)
+            settings->host_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
+        else {
+            guac_user_log(user, GUAC_LOG_WARNING, "Invalid host key type specified %s.  "
+                    "Ignoring host key.", str_host_key_type);
+            settings->host_key = NULL;
+        }
+    }
+
     settings->username =
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_USERNAME, NULL);
@@ -404,7 +417,6 @@ void guac_ssh_settings_free(guac_ssh_settings* settings) {
 
     /* Free network connection information */
     free(settings->hostname);
-    free(settings->host_key_type);
     free(settings->host_key);
     free(settings->port);
 
@@ -439,4 +451,3 @@ void guac_ssh_settings_free(guac_ssh_settings* settings) {
     free(settings);
 
 }
-
diff --git a/src/protocols/ssh/settings.h b/src/protocols/ssh/settings.h
index ac8400ec..e47a8161 100644
--- a/src/protocols/ssh/settings.h
+++ b/src/protocols/ssh/settings.h
@@ -73,7 +73,7 @@ typedef struct guac_ssh_settings {
     /**
      * The type of public SSH host key.
      */
-    char* host_key_type;
+    int host_key_type;
 
     /**
      * The public SSH host key.
diff --git a/src/protocols/ssh/ssh.c b/src/protocols/ssh/ssh.c
index a614f813..63765559 100644
--- a/src/protocols/ssh/ssh.c
+++ b/src/protocols/ssh/ssh.c
@@ -235,7 +235,8 @@ void* ssh_client_thread(void* data) {
 
     /* Open SSH session */
     ssh_client->session = guac_common_ssh_create_session(client,
-            settings->hostname, settings->port, ssh_client->user, settings->server_alive_interval);
+            settings->hostname, settings->port, ssh_client->user, settings->server_alive_interval,
+            settings->host_key_type, settings->host_key);
     if (ssh_client->session == NULL) {
         /* Already aborted within guac_common_ssh_create_session() */
         return NULL;
@@ -275,7 +276,8 @@ void* ssh_client_thread(void* data) {
         guac_client_log(client, GUAC_LOG_DEBUG, "Reconnecting for SFTP...");
         ssh_client->sftp_session =
             guac_common_ssh_create_session(client, settings->hostname,
-                    settings->port, ssh_client->user, settings->server_alive_interval);
+                    settings->port, ssh_client->user, settings->server_alive_interval,
+                    settings->host_key_type, settings->host_key);
         if (ssh_client->sftp_session == NULL) {
             /* Already aborted within guac_common_ssh_create_session() */
             return NULL;
diff --git a/src/protocols/vnc/settings.c b/src/protocols/vnc/settings.c
index 509921a5..509a067b 100644
--- a/src/protocols/vnc/settings.c
+++ b/src/protocols/vnc/settings.c
@@ -24,6 +24,9 @@
 
 #include <guacamole/user.h>
 
+#ifdef ENABLE_COMMON_SSH
+#include <libssh2.h>
+#endif
 #include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
@@ -208,6 +211,16 @@ enum VNC_ARGS_IDX {
      */
     IDX_SFTP_USERNAME,
 
+    /**
+     * The type of public SSH host key provided to identify the SFTP server.
+     */
+    IDX_SFTP_HOST_KEY_TYPE,
+
+    /**
+     * The public SSH host key to identify the SFTP server.
+     */
+    IDX_SFTP_HOST_KEY,
+
     /**
      * The password to provide when authenticating with the SSH server for
      * SFTP (if not using a private key).
@@ -411,6 +424,30 @@ guac_vnc_settings* guac_vnc_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
                 IDX_SFTP_HOSTNAME, settings->hostname);
 
+    /* The public SSH host key. */
+    settings->sftp_host_key =
+        guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                IDX_SFTP_HOST_KEY, NULL);
+
+    if(settings->sftp_host_key) {
+        /* Type of public SSH host key. */
+        char* str_host_key_type = guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
+                    IDX_SFTP_HOST_KEY_TYPE, "ssh-rsa");
+
+        if (strcmp(str_host_key_type, "ssh-rsa") == 0)
+            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
+        else if (strcmp(str_host_key_type, "ssh-dss") == 0)
+            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
+        else if (strcmp(str_host_key_type, "rsa1") == 0)
+            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
+        else {
+            guac_user_log(user, GUAC_LOG_WARNING, "Invalid host key type specified %s.  "
+                    "Ignoring host key.", str_host_key_type);
+            settings->sftp_host_key = NULL;
+        }
+
+    }
+
     /* Port for SFTP connection */
     settings->sftp_port =
         guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
diff --git a/src/protocols/vnc/settings.h b/src/protocols/vnc/settings.h
index 85e6478c..35809f83 100644
--- a/src/protocols/vnc/settings.h
+++ b/src/protocols/vnc/settings.h
@@ -138,6 +138,16 @@ typedef struct guac_vnc_settings {
      */
     char* sftp_hostname;
 
+    /**
+     * The type of public SSH host key provided.
+     */
+    int sftp_host_key_type;
+
+    /**
+     * The public SSH host key.
+     */
+    char* sftp_host_key;
+
     /**
      * The port of the SSH server to connect to for SFTP.
      */
diff --git a/src/protocols/vnc/vnc.c b/src/protocols/vnc/vnc.c
index db1e2180..1146ad43 100644
--- a/src/protocols/vnc/vnc.c
+++ b/src/protocols/vnc/vnc.c
@@ -261,7 +261,8 @@ void* guac_vnc_client_thread(void* data) {
         /* Attempt SSH connection */
         vnc_client->sftp_session =
             guac_common_ssh_create_session(client, settings->sftp_hostname,
-                    settings->sftp_port, vnc_client->sftp_user, settings->sftp_server_alive_interval);
+                    settings->sftp_port, vnc_client->sftp_user, settings->sftp_server_alive_interval,
+                    settings->sftp_host_key_type, settings->sftp_host_key);
 
         /* Fail if SSH connection does not succeed */
         if (vnc_client->sftp_session == NULL) {

From 2f0c6dcfa3647960fa2b64c149b410a395edb6a9 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Thu, 5 Apr 2018 11:26:50 -0400
Subject: [PATCH 04/20] GUACAMOLE-527: Add error logging for known host checks.

---
 src/common-ssh/ssh.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 0eb9fa10..ee60ccf9 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -534,11 +534,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     int fp_type;
     const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
 
-    if (!fingerprint || strcmp(fingerprint, "") == 0) {
-        guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Could not retrieve fingerprint of SSH server %s", hostname);
-    }
-
+    /* Check fingerprint against known hosts */
     struct libssh2_knownhost *host;
     int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
                                          fingerprint, fp_len,
@@ -552,15 +548,23 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
                 "Host key match found.");
             break;
         case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
+            guac_client_log(client, GUAC_LOG_ERROR,
+                "Host key not found in known hosts entries for %s.", hostname);
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host key not found in known hosts file.");
+                "Host key not found in known hosts entries.");
             break;
         case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+            guac_client_log(client, GUAC_LOG_ERROR,
+                "Host entry found, but host key does not match for %s",
+                hostname);
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
                 "Host key does not match host entry.");
             break;
         case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
         default:
+            guac_client_log(client, GUAC_LOG_ERROR,
+                "Error checking host key against known hosts for %s",
+                hostname);
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
                 "Host could not be checked against known hosts.");
     }

From c080569cacc6c3c31d339e234e6e69966b696397 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Thu, 5 Apr 2018 11:28:32 -0400
Subject: [PATCH 05/20] GUACAMOLE-527: Fix issue with null host_key variable.

---
 src/common-ssh/ssh.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index ee60ccf9..01d50003 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -520,7 +520,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
 
     /* Add host key provided from settings */
-    if (strcmp(host_key, "") > 0) {
+    if (host_key && strcmp(host_key, "") > 0) {
 
         if (libssh2_knownhost_addc(ssh_known_hosts, hostname, NULL, host_key, strlen(host_key),
                 NULL, 0, LIBSSH2_KNOWNHOST_TYPE_PLAIN|LIBSSH2_KNOWNHOST_KEYENC_BASE64|

From 5bb616832e34bc207cff142f24c1a7732f003d47 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Fri, 6 Apr 2018 05:45:14 -0400
Subject: [PATCH 06/20] GUACAMOLE-527: Order SSH handshake correctly, and
 remove unnecessary logging.

---
 src/common-ssh/ssh.c | 40 +++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 01d50003..1327b03e 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -511,6 +511,15 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         return NULL;
     }
 
+    /* Perform handshake */
+    if (libssh2_session_handshake(session, fd)) {
+        guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,
+                "SSH handshake failed.");
+        free(common_session);
+        close(fd);
+        return NULL;
+    }
+
     /* Check known_hosts */
     /* Get known hosts file from user running guacd */
     struct passwd *pw = getpwuid(getuid());
@@ -527,6 +536,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
                          host_key_type, NULL))
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
                 "Failed to add host key to known hosts store for %s", hostname);
+
     }
 
     /* Get fingerprint of host we're connecting to */
@@ -534,6 +544,10 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     int fp_type;
     const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
 
+    if (!fingerprint)
+        guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Failed to get fingerprint for host %s", hostname);
+
     /* Check fingerprint against known hosts */
     struct libssh2_knownhost *host;
     int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
@@ -545,37 +559,21 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     switch (kh_check) {
         case LIBSSH2_KNOWNHOST_CHECK_MATCH:
             guac_client_log(client, GUAC_LOG_DEBUG,
-                "Host key match found.");
+                "Host key match found for %s", hostname);
             break;
         case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
-            guac_client_log(client, GUAC_LOG_ERROR,
-                "Host key not found in known hosts entries for %s.", hostname);
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host key not found in known hosts entries.");
+                "Host key not found for %s.", hostname);
             break;
         case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
-            guac_client_log(client, GUAC_LOG_ERROR,
-                "Host entry found, but host key does not match for %s",
-                hostname);
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host key does not match host entry.");
+                "Host key does not match host entry for %s", hostname);
             break;
         case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
         default:
-            guac_client_log(client, GUAC_LOG_ERROR,
-                "Error checking host key against known hosts for %s",
-                hostname);
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host could not be checked against known hosts.");
-    }
-
-    /* Perform handshake */
-    if (libssh2_session_handshake(session, fd)) {
-        guac_client_abort(client, GUAC_PROTOCOL_STATUS_UPSTREAM_ERROR,
-                "SSH handshake failed.");
-        free(common_session);
-        close(fd);
-        return NULL;
+                "Host %s could not be checked against known hosts.",
+                hostname);
     }
 
     /* Store basic session data */

From ec4315dfbe9a648a5cb18c74f4dda7f0380a162a Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Fri, 6 Apr 2018 06:33:24 -0400
Subject: [PATCH 07/20] GUACAMOLE-527: Correct names of parameters coming from
 client.

---
 src/protocols/ssh/settings.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index 4653e96f..d49a16c1 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -32,8 +32,8 @@
 /* Client plugin arguments */
 const char* GUAC_SSH_CLIENT_ARGS[] = {
     "hostname",
-    "host_key_type",
-    "host_key",
+    "host-key-type",
+    "host-key",
     "port",
     "username",
     "password",

From 42044e42799402898c00ace8ca770c94f6799843 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Fri, 6 Apr 2018 06:47:35 -0400
Subject: [PATCH 08/20] GUACAMOLE-527: Clean up memory and logging.

---
 src/common-ssh/ssh.c             | 18 ++++++++++--------
 src/protocols/rdp/rdp_settings.c |  3 +++
 src/protocols/ssh/settings.c     |  2 ++
 src/protocols/vnc/settings.c     |  3 +++
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 1327b03e..03c4d125 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -520,22 +520,22 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         return NULL;
     }
 
-    /* Check known_hosts */
-    /* Get known hosts file from user running guacd */
+    /* Check known_hosts, start by getting known_hosts file of user running guacd */
     struct passwd *pw = getpwuid(getuid());
-    char *homedir = pw->pw_dir;
-    char *known_hosts = strcat(homedir, "/.ssh/known_hosts");
+    const char *known_hosts = strcat(pw->pw_dir, "/.ssh/known_hosts");
     LIBSSH2_KNOWNHOSTS *ssh_known_hosts = libssh2_knownhost_init(session);
     libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
 
     /* Add host key provided from settings */
     if (host_key && strcmp(host_key, "") > 0) {
 
-        if (libssh2_knownhost_addc(ssh_known_hosts, hostname, NULL, host_key, strlen(host_key),
+        int kh_add = libssh2_knownhost_addc(ssh_known_hosts, hostname, NULL, host_key, strlen(host_key),
                 NULL, 0, LIBSSH2_KNOWNHOST_TYPE_PLAIN|LIBSSH2_KNOWNHOST_KEYENC_BASE64|
-                         host_key_type, NULL))
-            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Failed to add host key to known hosts store for %s", hostname);
+                         host_key_type, NULL);
+
+        if (kh_add)
+            guac_client_log(client, GUAC_LOG_WARNING, "Failed to add provided host key"
+                    " to known hosts store for %s.  Error was %d", hostname, kh_add);
 
     }
 
@@ -556,6 +556,8 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
                                          LIBSSH2_KNOWNHOST_KEYENC_RAW,
                                          &host);
 
+    libssh2_knownhost_free(ssh_known_hosts);
+
     switch (kh_check) {
         case LIBSSH2_KNOWNHOST_CHECK_MATCH:
             guac_client_log(client, GUAC_LOG_DEBUG,
diff --git a/src/protocols/rdp/rdp_settings.c b/src/protocols/rdp/rdp_settings.c
index 78afe374..65e79e6b 100644
--- a/src/protocols/rdp/rdp_settings.c
+++ b/src/protocols/rdp/rdp_settings.c
@@ -860,6 +860,8 @@ guac_rdp_settings* guac_rdp_parse_args(guac_user* user,
             settings->sftp_host_key = NULL;
         }
 
+        free(str_host_key_type);
+
     }
 
     /* Port for SFTP connection */
@@ -1039,6 +1041,7 @@ void guac_rdp_settings_free(guac_rdp_settings* settings) {
     /* Free SFTP settings */
     free(settings->sftp_directory);
     free(settings->sftp_root_directory);
+    free(settings->sftp_host_key);
     free(settings->sftp_hostname);
     free(settings->sftp_passphrase);
     free(settings->sftp_password);
diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index d49a16c1..119d725d 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -278,6 +278,8 @@ guac_ssh_settings* guac_ssh_parse_args(guac_user* user,
                     "Ignoring host key.", str_host_key_type);
             settings->host_key = NULL;
         }
+
+        free(str_host_key_type);
     }
 
     settings->username =
diff --git a/src/protocols/vnc/settings.c b/src/protocols/vnc/settings.c
index 509a067b..5f82b39b 100644
--- a/src/protocols/vnc/settings.c
+++ b/src/protocols/vnc/settings.c
@@ -446,6 +446,8 @@ guac_vnc_settings* guac_vnc_parse_args(guac_user* user,
             settings->sftp_host_key = NULL;
         }
 
+        free(str_host_key_type);
+
     }
 
     /* Port for SFTP connection */
@@ -541,6 +543,7 @@ void guac_vnc_settings_free(guac_vnc_settings* settings) {
     /* Free SFTP settings */
     free(settings->sftp_directory);
     free(settings->sftp_root_directory);
+    free(settings->sftp_host_key);
     free(settings->sftp_hostname);
     free(settings->sftp_passphrase);
     free(settings->sftp_password);

From 551598e0a4fcea547fcd050b278e0c4e6114842f Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Tue, 22 May 2018 22:59:51 -0400
Subject: [PATCH 09/20] GUACAMOLE-527: Use libssh2_knownhost_readline and
 remove host key type.

---
 src/common-ssh/common-ssh/ssh.h  |  2 +-
 src/common-ssh/ssh.c             |  9 ++++-----
 src/protocols/rdp/rdp.c          |  2 +-
 src/protocols/rdp/rdp_settings.c | 27 ---------------------------
 src/protocols/rdp/rdp_settings.h |  5 -----
 src/protocols/ssh/settings.c     | 23 -----------------------
 src/protocols/ssh/settings.h     |  5 -----
 src/protocols/ssh/ssh.c          |  4 ++--
 src/protocols/vnc/settings.c     | 26 --------------------------
 src/protocols/vnc/settings.h     |  5 -----
 src/protocols/vnc/vnc.c          |  2 +-
 11 files changed, 9 insertions(+), 101 deletions(-)

diff --git a/src/common-ssh/common-ssh/ssh.h b/src/common-ssh/common-ssh/ssh.h
index 8f6f6893..672e7767 100644
--- a/src/common-ssh/common-ssh/ssh.h
+++ b/src/common-ssh/common-ssh/ssh.h
@@ -99,7 +99,7 @@ void guac_common_ssh_uninit();
  */
 guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive,
-        const int host_key_type, const char* host_key);
+        const char* host_key);
 
 /**
  * Disconnects and destroys the given SSH session, freeing all associated
diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 03c4d125..54eae3b0 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -416,7 +416,7 @@ static int guac_common_ssh_authenticate(guac_common_ssh_session* common_session)
 
 guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         const char* hostname, const char* port, guac_common_ssh_user* user, int keepalive,
-        const int host_key_type, const char* host_key) {
+        const char* host_key) {
 
     int retval;
 
@@ -529,9 +529,8 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     /* Add host key provided from settings */
     if (host_key && strcmp(host_key, "") > 0) {
 
-        int kh_add = libssh2_knownhost_addc(ssh_known_hosts, hostname, NULL, host_key, strlen(host_key),
-                NULL, 0, LIBSSH2_KNOWNHOST_TYPE_PLAIN|LIBSSH2_KNOWNHOST_KEYENC_BASE64|
-                         host_key_type, NULL);
+        int kh_add = libssh2_knownhost_readline(ssh_known_hosts, host_key, strlen(host_key),
+                LIBSSH2_KNOWNHOST_FILE_OPENSSH);
 
         if (kh_add)
             guac_client_log(client, GUAC_LOG_WARNING, "Failed to add provided host key"
@@ -564,7 +563,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
                 "Host key match found for %s", hostname);
             break;
         case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
-            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+            guac_client_log(client, GUAC_LOG_WARNING,
                 "Host key not found for %s.", hostname);
             break;
         case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
diff --git a/src/protocols/rdp/rdp.c b/src/protocols/rdp/rdp.c
index 30b19326..4d484320 100644
--- a/src/protocols/rdp/rdp.c
+++ b/src/protocols/rdp/rdp.c
@@ -975,7 +975,7 @@ void* guac_rdp_client_thread(void* data) {
         rdp_client->sftp_session =
             guac_common_ssh_create_session(client, settings->sftp_hostname,
                     settings->sftp_port, rdp_client->sftp_user, settings->sftp_server_alive_interval,
-                    settings->sftp_host_key_type, settings->sftp_host_key);
+                    settings->sftp_host_key);
 
         /* Fail if SSH connection does not succeed */
         if (rdp_client->sftp_session == NULL) {
diff --git a/src/protocols/rdp/rdp_settings.c b/src/protocols/rdp/rdp_settings.c
index 65e79e6b..2fe261ce 100644
--- a/src/protocols/rdp/rdp_settings.c
+++ b/src/protocols/rdp/rdp_settings.c
@@ -360,12 +360,6 @@ enum RDP_ARGS_IDX {
      */
     IDX_SFTP_HOSTNAME,
 
-    /**
-     * The type of public SSH host key provided.  If not specified, it defaults
-     * to SSH-RSA.
-     */
-    IDX_SFTP_HOST_KEY_TYPE,
-
     /**
      * The public SSH host key of the SFTP server.  Optional.
      */
@@ -843,27 +837,6 @@ guac_rdp_settings* guac_rdp_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
                 IDX_SFTP_HOST_KEY, NULL);
 
-    if(settings->sftp_host_key) {
-        /* Type of public SSH host key. */
-        char* str_host_key_type = guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
-                    IDX_SFTP_HOST_KEY_TYPE, "ssh-rsa");
-        
-        if (strcmp(str_host_key_type, "ssh-rsa") == 0)
-            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
-        else if (strcmp(str_host_key_type, "ssh-dss") == 0)
-            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
-        else if (strcmp(str_host_key_type, "rsa1") == 0)
-            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
-        else {
-            guac_user_log(user, GUAC_LOG_WARNING, "Invalid host key type specified %s.  "
-                    "Ignoring host key.", str_host_key_type);
-            settings->sftp_host_key = NULL;
-        }
-
-        free(str_host_key_type);
-
-    }
-
     /* Port for SFTP connection */
     settings->sftp_port =
         guac_user_parse_args_string(user, GUAC_RDP_CLIENT_ARGS, argv,
diff --git a/src/protocols/rdp/rdp_settings.h b/src/protocols/rdp/rdp_settings.h
index 0a442799..4f3839e6 100644
--- a/src/protocols/rdp/rdp_settings.h
+++ b/src/protocols/rdp/rdp_settings.h
@@ -342,11 +342,6 @@ typedef struct guac_rdp_settings {
      */
     char* sftp_hostname;
 
-    /**
-     * The type of the public SSH hos key.
-     */
-    int sftp_host_key_type;
-
     /**
      * The public SSH host key.
      */
diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index 119d725d..4a1c3710 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -71,11 +71,6 @@ enum SSH_ARGS_IDX {
      */
     IDX_HOSTNAME,
 
-    /**
-     * The type of public SSH host key provided.  Optional.
-     */
-    IDX_HOST_KEY_TYPE,
-
     /**
      * The Base64-encoded public SSH host key.  Optional.
      */
@@ -264,24 +259,6 @@ guac_ssh_settings* guac_ssh_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_HOST_KEY, NULL);
 
-    if (settings->host_key) {
-        char* str_host_key_type = guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
-                    IDX_HOST_KEY_TYPE, "ssh-rsa");
-        if (strcmp(str_host_key_type, "ssh-rsa") == 0)
-            settings->host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
-        else if (strcmp(str_host_key_type, "ssh-dss") == 0)
-            settings->host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
-        else if (strcmp(str_host_key_type, "rsa1") == 0)
-            settings->host_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
-        else {
-            guac_user_log(user, GUAC_LOG_WARNING, "Invalid host key type specified %s.  "
-                    "Ignoring host key.", str_host_key_type);
-            settings->host_key = NULL;
-        }
-
-        free(str_host_key_type);
-    }
-
     settings->username =
         guac_user_parse_args_string(user, GUAC_SSH_CLIENT_ARGS, argv,
                 IDX_USERNAME, NULL);
diff --git a/src/protocols/ssh/settings.h b/src/protocols/ssh/settings.h
index e47a8161..761239c7 100644
--- a/src/protocols/ssh/settings.h
+++ b/src/protocols/ssh/settings.h
@@ -70,11 +70,6 @@ typedef struct guac_ssh_settings {
      */
     char* hostname;
 
-    /**
-     * The type of public SSH host key.
-     */
-    int host_key_type;
-
     /**
      * The public SSH host key.
      */
diff --git a/src/protocols/ssh/ssh.c b/src/protocols/ssh/ssh.c
index 63765559..f98f2228 100644
--- a/src/protocols/ssh/ssh.c
+++ b/src/protocols/ssh/ssh.c
@@ -236,7 +236,7 @@ void* ssh_client_thread(void* data) {
     /* Open SSH session */
     ssh_client->session = guac_common_ssh_create_session(client,
             settings->hostname, settings->port, ssh_client->user, settings->server_alive_interval,
-            settings->host_key_type, settings->host_key);
+            settings->host_key);
     if (ssh_client->session == NULL) {
         /* Already aborted within guac_common_ssh_create_session() */
         return NULL;
@@ -277,7 +277,7 @@ void* ssh_client_thread(void* data) {
         ssh_client->sftp_session =
             guac_common_ssh_create_session(client, settings->hostname,
                     settings->port, ssh_client->user, settings->server_alive_interval,
-                    settings->host_key_type, settings->host_key);
+                    settings->host_key);
         if (ssh_client->sftp_session == NULL) {
             /* Already aborted within guac_common_ssh_create_session() */
             return NULL;
diff --git a/src/protocols/vnc/settings.c b/src/protocols/vnc/settings.c
index 5f82b39b..130c97d5 100644
--- a/src/protocols/vnc/settings.c
+++ b/src/protocols/vnc/settings.c
@@ -211,11 +211,6 @@ enum VNC_ARGS_IDX {
      */
     IDX_SFTP_USERNAME,
 
-    /**
-     * The type of public SSH host key provided to identify the SFTP server.
-     */
-    IDX_SFTP_HOST_KEY_TYPE,
-
     /**
      * The public SSH host key to identify the SFTP server.
      */
@@ -429,27 +424,6 @@ guac_vnc_settings* guac_vnc_parse_args(guac_user* user,
         guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
                 IDX_SFTP_HOST_KEY, NULL);
 
-    if(settings->sftp_host_key) {
-        /* Type of public SSH host key. */
-        char* str_host_key_type = guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
-                    IDX_SFTP_HOST_KEY_TYPE, "ssh-rsa");
-
-        if (strcmp(str_host_key_type, "ssh-rsa") == 0)
-            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
-        else if (strcmp(str_host_key_type, "ssh-dss") == 0)
-            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_SSHDSS;
-        else if (strcmp(str_host_key_type, "rsa1") == 0)
-            settings->sftp_host_key_type = LIBSSH2_KNOWNHOST_KEY_RSA1;
-        else {
-            guac_user_log(user, GUAC_LOG_WARNING, "Invalid host key type specified %s.  "
-                    "Ignoring host key.", str_host_key_type);
-            settings->sftp_host_key = NULL;
-        }
-
-        free(str_host_key_type);
-
-    }
-
     /* Port for SFTP connection */
     settings->sftp_port =
         guac_user_parse_args_string(user, GUAC_VNC_CLIENT_ARGS, argv,
diff --git a/src/protocols/vnc/settings.h b/src/protocols/vnc/settings.h
index 35809f83..3e2ebd5e 100644
--- a/src/protocols/vnc/settings.h
+++ b/src/protocols/vnc/settings.h
@@ -138,11 +138,6 @@ typedef struct guac_vnc_settings {
      */
     char* sftp_hostname;
 
-    /**
-     * The type of public SSH host key provided.
-     */
-    int sftp_host_key_type;
-
     /**
      * The public SSH host key.
      */
diff --git a/src/protocols/vnc/vnc.c b/src/protocols/vnc/vnc.c
index 1146ad43..d9f9dbbb 100644
--- a/src/protocols/vnc/vnc.c
+++ b/src/protocols/vnc/vnc.c
@@ -262,7 +262,7 @@ void* guac_vnc_client_thread(void* data) {
         vnc_client->sftp_session =
             guac_common_ssh_create_session(client, settings->sftp_hostname,
                     settings->sftp_port, vnc_client->sftp_user, settings->sftp_server_alive_interval,
-                    settings->sftp_host_key_type, settings->sftp_host_key);
+                    settings->sftp_host_key);
 
         /* Fail if SSH connection does not succeed */
         if (vnc_client->sftp_session == NULL) {

From 2bebb96804f1bf6d0f573de53999f8ee8e368ef3 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Thu, 24 May 2018 09:24:48 -0400
Subject: [PATCH 10/20] GUACAMOLE-527: Fix host key options in the protocol
 settings.

---
 src/protocols/rdp/rdp_settings.c | 1 -
 src/protocols/ssh/settings.c     | 1 -
 src/protocols/vnc/settings.c     | 1 +
 3 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/protocols/rdp/rdp_settings.c b/src/protocols/rdp/rdp_settings.c
index 2fe261ce..0af64437 100644
--- a/src/protocols/rdp/rdp_settings.c
+++ b/src/protocols/rdp/rdp_settings.c
@@ -84,7 +84,6 @@ const char* GUAC_RDP_CLIENT_ARGS[] = {
 #ifdef ENABLE_COMMON_SSH
     "enable-sftp",
     "sftp-hostname",
-    "sftp-host-key-type",
     "sftp-host-key",
     "sftp-port",
     "sftp-username",
diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index 4a1c3710..7820cf63 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -32,7 +32,6 @@
 /* Client plugin arguments */
 const char* GUAC_SSH_CLIENT_ARGS[] = {
     "hostname",
-    "host-key-type",
     "host-key",
     "port",
     "username",
diff --git a/src/protocols/vnc/settings.c b/src/protocols/vnc/settings.c
index 130c97d5..27524e13 100644
--- a/src/protocols/vnc/settings.c
+++ b/src/protocols/vnc/settings.c
@@ -63,6 +63,7 @@ const char* GUAC_VNC_CLIENT_ARGS[] = {
 #ifdef ENABLE_COMMON_SSH
     "enable-sftp",
     "sftp-hostname",
+    "sftp-host-key",
     "sftp-port",
     "sftp-username",
     "sftp-password",

From aec2be6da28fb0e58474e2c2bdd32989330bedb9 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Thu, 24 May 2018 09:41:44 -0400
Subject: [PATCH 11/20] GUACAMOLE-527: Remove unnecessary includes.

---
 src/protocols/rdp/rdp_settings.c | 3 ---
 src/protocols/ssh/settings.c     | 1 -
 src/protocols/vnc/settings.c     | 3 ---
 3 files changed, 7 deletions(-)

diff --git a/src/protocols/rdp/rdp_settings.c b/src/protocols/rdp/rdp_settings.c
index 0af64437..e1358303 100644
--- a/src/protocols/rdp/rdp_settings.c
+++ b/src/protocols/rdp/rdp_settings.c
@@ -35,9 +35,6 @@
 #include "compat/winpr-wtypes.h"
 #endif
 
-#ifdef ENABLE_COMMON_SSH
-#include <libssh2.h>
-#endif
 #include <stddef.h>
 #include <string.h>
 
diff --git a/src/protocols/ssh/settings.c b/src/protocols/ssh/settings.c
index 7820cf63..7cfe404f 100644
--- a/src/protocols/ssh/settings.c
+++ b/src/protocols/ssh/settings.c
@@ -24,7 +24,6 @@
 
 #include <guacamole/user.h>
 
-#include <libssh2.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
diff --git a/src/protocols/vnc/settings.c b/src/protocols/vnc/settings.c
index 27524e13..587864a4 100644
--- a/src/protocols/vnc/settings.c
+++ b/src/protocols/vnc/settings.c
@@ -24,9 +24,6 @@
 
 #include <guacamole/user.h>
 
-#ifdef ENABLE_COMMON_SSH
-#include <libssh2.h>
-#endif
 #include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>

From ac2b4f8d12e89cc6accc6b0f8649dd66075be64a Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Sun, 27 May 2018 16:46:36 -0400
Subject: [PATCH 12/20] GUACAMOLE-527: Check either provided key or key file,
 if it exists.

---
 src/common-ssh/ssh.c | 86 ++++++++++++++++++++++++--------------------
 1 file changed, 47 insertions(+), 39 deletions(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 54eae3b0..4bd3a3dc 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -520,17 +520,16 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         return NULL;
     }
 
-    /* Check known_hosts, start by getting known_hosts file of user running guacd */
-    struct passwd *pw = getpwuid(getuid());
-    const char *known_hosts = strcat(pw->pw_dir, "/.ssh/known_hosts");
+    /* SSH known host key checking. */
     LIBSSH2_KNOWNHOSTS *ssh_known_hosts = libssh2_knownhost_init(session);
-    libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+    int num_known_hosts = 0;
 
     /* Add host key provided from settings */
-    if (host_key && strcmp(host_key, "") > 0) {
+    if (host_key && strcmp(host_key, "") != 0) {
 
         int kh_add = libssh2_knownhost_readline(ssh_known_hosts, host_key, strlen(host_key),
                 LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+        num_known_hosts++;
 
         if (kh_add)
             guac_client_log(client, GUAC_LOG_WARNING, "Failed to add provided host key"
@@ -538,43 +537,52 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
 
     }
 
-    /* Get fingerprint of host we're connecting to */
-    size_t fp_len;
-    int fp_type;
-    const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
+    /* Otherwise, we look for a ssh_known_hosts file within GUACAMOLE_HOME and read that in. */
+    else {
+        const char *known_hosts = "/etc/guacamole/ssh_known_hosts";
+        num_known_hosts = libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+    }
 
-    if (!fingerprint)
-        guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Failed to get fingerprint for host %s", hostname);
+    /* If we've found a provided set of host keys, check against them. */
+    if (num_known_hosts > 0) {
+        /* Get fingerprint of host we're connecting to */
+        size_t fp_len;
+        int fp_type;
+        const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
 
-    /* Check fingerprint against known hosts */
-    struct libssh2_knownhost *host;
-    int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
-                                         fingerprint, fp_len,
-                                         LIBSSH2_KNOWNHOST_TYPE_PLAIN|
-                                         LIBSSH2_KNOWNHOST_KEYENC_RAW,
-                                         &host);
-
-    libssh2_knownhost_free(ssh_known_hosts);
-
-    switch (kh_check) {
-        case LIBSSH2_KNOWNHOST_CHECK_MATCH:
-            guac_client_log(client, GUAC_LOG_DEBUG,
-                "Host key match found for %s", hostname);
-            break;
-        case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
-            guac_client_log(client, GUAC_LOG_WARNING,
-                "Host key not found for %s.", hostname);
-            break;
-        case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+        if (!fingerprint)
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host key does not match host entry for %s", hostname);
-            break;
-        case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
-        default:
-            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host %s could not be checked against known hosts.",
-                hostname);
+                    "Failed to get fingerprint for host %s", hostname);
+
+        /* Check fingerprint against known hosts */
+        struct libssh2_knownhost *host;
+        int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
+                                             fingerprint, fp_len,
+                                             LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                             LIBSSH2_KNOWNHOST_KEYENC_RAW,
+                                             &host);
+
+        libssh2_knownhost_free(ssh_known_hosts);
+
+        switch (kh_check) {
+            case LIBSSH2_KNOWNHOST_CHECK_MATCH:
+                guac_client_log(client, GUAC_LOG_DEBUG,
+                    "Host key match found for %s", hostname);
+                break;
+            case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Host key not found for %s.", hostname);
+                break;
+            case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Host key does not match known hosts entry for %s", hostname);
+                break;
+            case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
+            default:
+                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                    "Host %s could not be checked against known hosts.",
+                    hostname);
+        }
     }
 
     /* Store basic session data */

From 428243bb783ac58ecf228a5704b5709c26d9239b Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Mon, 28 May 2018 10:12:07 -0400
Subject: [PATCH 13/20] GUACAMOLE-527: Move host key checking to a separate
 function.

---
 src/common-ssh/common-ssh/key.h | 50 ++++++++++++++++++++
 src/common-ssh/key.c            | 78 +++++++++++++++++++++++++++++++
 src/common-ssh/ssh.c            | 83 +++++++++++----------------------
 3 files changed, 154 insertions(+), 57 deletions(-)

diff --git a/src/common-ssh/common-ssh/key.h b/src/common-ssh/common-ssh/key.h
index 1754deae..576ba1ba 100644
--- a/src/common-ssh/common-ssh/key.h
+++ b/src/common-ssh/common-ssh/key.h
@@ -22,6 +22,9 @@
 
 #include "config.h"
 
+#include <guacamole/client.h>
+#include <libssh2.h>
+
 #include <openssl/ossl_typ.h>
 
 /**
@@ -166,5 +169,52 @@ void guac_common_ssh_key_free(guac_common_ssh_key* key);
 int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
         int length, unsigned char* sig);
 
+/**
+ * Verifies the fingerprint for the given hostname/port combination against
+ * one or more known_hosts entries.  The known_host entries can either be a
+ * single host_key, provided by the client, or a set of known_hosts entries
+ * provided in the /etc/guacamole/ssh_known_hosts file.  Failure to correctly
+ * load the known_hosts entries will result in a connection abort and a returned
+ * error code.  A return code of zero indiciates that either no known_hosts entries
+ * were provided, or that the verification succeeded (match).  Negative values
+ * indicate internal libssh2 error codes; positive values indicate a failure
+ * during verification of the fingerprint against the known hosts.
+ *
+ * @param session
+ *     A pointer to the LIBSSH2_SESSION structure of the SSH connection already
+ *     in progress.
+ *
+ * @param client
+ *     The current guac_client instance for which the known_hosts checking is
+ *     being performed.
+ *
+ * @param host_key
+ *     The known host entry provided by the client.  If this is non-null and not
+ *     empty, it will be the only host key loaded and used for verification.  If
+ *     this is null or empty an attempt will be made to read the
+ *     /etc/guacamole/ssh_known_hosts file and load entries from it.
+ *
+ * @param hostname
+ *     The hostname or IP of the server that is being verified.
+ *
+ * @param port
+ *     The port number of the server being verified.
+ *
+ * @param fingerprint
+ *     The fingering of the server being verified.
+ *
+ * @param fp_len
+ *     The length of the fingerprint being verified
+ *
+ * @return
+ *     The status of the known_hosts check.  This will be zero if no entries
+ *     are provided or if the match succeeds, negative to indicate internal
+ *     libssh2 errors, or positive to indicate failures during host key
+ *     checking.
+ */
+int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* client,
+        const char* host_key, const char* hostname, int port, const char* fingerprint,
+        const size_t fp_len);
+
 #endif
 
diff --git a/src/common-ssh/key.c b/src/common-ssh/key.c
index a05d696d..570da8e8 100644
--- a/src/common-ssh/key.c
+++ b/src/common-ssh/key.c
@@ -245,3 +245,81 @@ int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
 
 }
 
+int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* client,
+        const char* host_key, const char* hostname, int port, const char* fingerprint,
+        const size_t fp_len) {
+
+    LIBSSH2_KNOWNHOSTS* ssh_known_hosts = libssh2_knownhost_init(session);
+    int known_hosts = 0;
+
+    /* Add host key provided from settings */
+    if (host_key && strcmp(host_key, "") != 0) {
+
+        known_hosts = libssh2_knownhost_readline(ssh_known_hosts, host_key, strlen(host_key),
+                LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+
+        /* readline function returns 0 on success, so we increment to indicate a valid entry */
+        if (known_hosts == 0)
+            known_hosts++;
+
+    }
+
+    /* Otherwise, we look for a ssh_known_hosts file within GUACAMOLE_HOME and read that in. */
+    else {
+
+        const char *guac_known_hosts = "/etc/guacamole/ssh_known_hosts";
+        known_hosts = libssh2_knownhost_readfile(ssh_known_hosts, guac_known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+
+    }
+
+    /* If there's an error provided, abort connection and return that. */
+    if (known_hosts < 0) {
+
+        guac_client_log(client, GUAC_LOG_ERROR,
+            "Failure trying to load SSH host keys.");
+
+        libssh2_knownhost_free(ssh_known_hosts);
+        return known_hosts;
+
+    }
+
+    /* No host keys were loaded, so we bail out checking and continue the connection. */
+    else if (known_hosts == 0) {
+        libssh2_knownhost_free(ssh_known_hosts);
+        return known_hosts;
+    }
+
+
+    /* Check fingerprint against known hosts */
+    int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, port,
+                                            fingerprint, fp_len,
+                                            LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                            LIBSSH2_KNOWNHOST_KEYENC_RAW,
+                                            NULL);
+
+    /* Deal with the return of the host key check */
+    switch (kh_check) {
+        case LIBSSH2_KNOWNHOST_CHECK_MATCH:
+            guac_client_log(client, GUAC_LOG_DEBUG,
+                "Host key match found for %s", hostname);
+            break;
+        case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
+            guac_client_log(client, GUAC_LOG_ERROR,
+                "Host key not found for %s.", hostname);
+            break;
+        case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
+            guac_client_log(client, GUAC_LOG_ERROR,
+                "Host key does not match known hosts entry for %s", hostname);
+            break;
+        case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
+        default:
+            guac_client_log(client, GUAC_LOG_ERROR,
+                "Host %s could not be checked against known hosts.",
+                hostname);
+    }
+
+    /* Return the check value */
+    libssh2_knownhost_free(ssh_known_hosts);
+    return kh_check;
+
+}
diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 4bd3a3dc..efdef838 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -520,69 +520,38 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         return NULL;
     }
 
+    /* Get fingerprint of host we're connecting to */
+    size_t fp_len;
+    int fp_type;
+    const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
+
+    /* Failure to generate a fingerprint means we should abort */
+    if (!fingerprint) {
+        guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+            "Failed to get fingerprint for host %s", hostname);
+        return NULL;
+    }
+
     /* SSH known host key checking. */
-    LIBSSH2_KNOWNHOSTS *ssh_known_hosts = libssh2_knownhost_init(session);
-    int num_known_hosts = 0;
+    int known_host_check = guac_common_ssh_verify_host_key(session, client, host_key,
+                                                           hostname, atoi(port), fingerprint,
+                                                           fp_len);
 
-    /* Add host key provided from settings */
-    if (host_key && strcmp(host_key, "") != 0) {
+    /* Abort on any error codes */
+    if (known_host_check != 0) {
+        char* err_msg;
+        int err_len;
+        libssh2_session_last_error(session, &err_msg, &err_len, 0);
 
-        int kh_add = libssh2_knownhost_readline(ssh_known_hosts, host_key, strlen(host_key),
-                LIBSSH2_KNOWNHOST_FILE_OPENSSH);
-        num_known_hosts++;
-
-        if (kh_add)
-            guac_client_log(client, GUAC_LOG_WARNING, "Failed to add provided host key"
-                    " to known hosts store for %s.  Error was %d", hostname, kh_add);
-
-    }
-
-    /* Otherwise, we look for a ssh_known_hosts file within GUACAMOLE_HOME and read that in. */
-    else {
-        const char *known_hosts = "/etc/guacamole/ssh_known_hosts";
-        num_known_hosts = libssh2_knownhost_readfile(ssh_known_hosts, known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
-    }
-
-    /* If we've found a provided set of host keys, check against them. */
-    if (num_known_hosts > 0) {
-        /* Get fingerprint of host we're connecting to */
-        size_t fp_len;
-        int fp_type;
-        const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
-
-        if (!fingerprint)
+        if (known_host_check < 0)
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Failed to get fingerprint for host %s", hostname);
+                "Error occurred attempting to check host key: %s", err_msg);
 
-        /* Check fingerprint against known hosts */
-        struct libssh2_knownhost *host;
-        int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, atoi(port),
-                                             fingerprint, fp_len,
-                                             LIBSSH2_KNOWNHOST_TYPE_PLAIN|
-                                             LIBSSH2_KNOWNHOST_KEYENC_RAW,
-                                             &host);
+        if (known_host_check > 0)
+            guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
+                "Host fingerprint did not match any provided known host keys: %s", err_msg);
 
-        libssh2_knownhost_free(ssh_known_hosts);
-
-        switch (kh_check) {
-            case LIBSSH2_KNOWNHOST_CHECK_MATCH:
-                guac_client_log(client, GUAC_LOG_DEBUG,
-                    "Host key match found for %s", hostname);
-                break;
-            case LIBSSH2_KNOWNHOST_CHECK_NOTFOUND:
-                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Host key not found for %s.", hostname);
-                break;
-            case LIBSSH2_KNOWNHOST_CHECK_MISMATCH:
-                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Host key does not match known hosts entry for %s", hostname);
-                break;
-            case LIBSSH2_KNOWNHOST_CHECK_FAILURE:
-            default:
-                guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                    "Host %s could not be checked against known hosts.",
-                    hostname);
-        }
+        return NULL;
     }
 
     /* Store basic session data */

From 27c977adb2a78e861a4fe5272ab8a41d8c3cd8c0 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Mon, 28 May 2018 10:23:47 -0400
Subject: [PATCH 14/20] GUACAMOLE-527: Make sure ssh_known_hosts exists before
 trying to load.

---
 src/common-ssh/key.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/common-ssh/key.c b/src/common-ssh/key.c
index 570da8e8..66b8386b 100644
--- a/src/common-ssh/key.c
+++ b/src/common-ssh/key.c
@@ -35,6 +35,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 guac_common_ssh_key* guac_common_ssh_key_alloc(char* data, int length,
         char* passphrase) {
@@ -268,7 +269,8 @@ int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* clien
     else {
 
         const char *guac_known_hosts = "/etc/guacamole/ssh_known_hosts";
-        known_hosts = libssh2_knownhost_readfile(ssh_known_hosts, guac_known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+        if (access(guac_known_hosts, F_OK) != -1)
+            known_hosts = libssh2_knownhost_readfile(ssh_known_hosts, guac_known_hosts, LIBSSH2_KNOWNHOST_FILE_OPENSSH);
 
     }
 

From ebbb7492e77e1d0e9f9f6e12269e723a330e8f63 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Mon, 28 May 2018 10:27:44 -0400
Subject: [PATCH 15/20] GUACAMOLE-527: Add warning if no known host keys are
 provided.

---
 src/common-ssh/key.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/common-ssh/key.c b/src/common-ssh/key.c
index 66b8386b..b7c73f08 100644
--- a/src/common-ssh/key.c
+++ b/src/common-ssh/key.c
@@ -287,6 +287,8 @@ int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* clien
 
     /* No host keys were loaded, so we bail out checking and continue the connection. */
     else if (known_hosts == 0) {
+        guac_client_log(client, GUAC_LOG_WARNING,
+            "No known host keys provided, host identity will not be verified.");
         libssh2_knownhost_free(ssh_known_hosts);
         return known_hosts;
     }

From 7e254955e8dc58f5d3d487ef45c05d6991a3792a Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Mon, 28 May 2018 10:31:34 -0400
Subject: [PATCH 16/20] GUACAMOLE-527: Slight tweak to error message.

---
 src/common-ssh/ssh.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index efdef838..4ed6d1d1 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -549,7 +549,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
 
         if (known_host_check > 0)
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host fingerprint did not match any provided known host keys: %s", err_msg);
+                "Host fingerprint did not match any provided known host keys. %s", err_msg);
 
         return NULL;
     }

From f9379dc6bb9d2dbdc280b99604ce0520f9b426ec Mon Sep 17 00:00:00 2001
From: Nick Couchman <nick_couchman@cotyinc.com>
Date: Mon, 25 Jun 2018 08:31:00 -0400
Subject: [PATCH 17/20] GUACAMOLE-527: Get full error message when key
 verification fails.

---
 src/common-ssh/key.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/common-ssh/key.c b/src/common-ssh/key.c
index b7c73f08..4d569db7 100644
--- a/src/common-ssh/key.c
+++ b/src/common-ssh/key.c
@@ -277,8 +277,10 @@ int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* clien
     /* If there's an error provided, abort connection and return that. */
     if (known_hosts < 0) {
 
+        char* errmsg;
+        int errval = libssh2_session_last_error(session, &errmsg, NULL, 0);
         guac_client_log(client, GUAC_LOG_ERROR,
-            "Failure trying to load SSH host keys.");
+            "Error %d trying to load SSH host keys: %s", errval, errmsg);
 
         libssh2_knownhost_free(ssh_known_hosts);
         return known_hosts;

From ba684962b6f19e4ddd0ffa1435f0fe8563b978a9 Mon Sep 17 00:00:00 2001
From: Nick Couchman <nick_couchman@cotyinc.com>
Date: Mon, 25 Jun 2018 13:50:19 -0400
Subject: [PATCH 18/20] GUACAMOLE-527: Plug some memory leaks before returning
 NULL.

---
 src/common-ssh/ssh.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 4ed6d1d1..1b13520c 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -529,6 +529,8 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     if (!fingerprint) {
         guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
             "Failed to get fingerprint for host %s", hostname);
+        free(common_session);
+        close(fd);
         return NULL;
     }
 
@@ -551,6 +553,8 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
                 "Host fingerprint did not match any provided known host keys. %s", err_msg);
 
+        free(common_session);
+        close(fd);
         return NULL;
     }
 

From 7bc6a623650b8b0d3c2e24d6b78cf288a81923a6 Mon Sep 17 00:00:00 2001
From: Nick Couchman <nick_couchman@cotyinc.com>
Date: Mon, 25 Jun 2018 13:57:01 -0400
Subject: [PATCH 19/20] GUACAMOLE-527: Do not call a remote host key a
 fingerprint.

---
 src/common-ssh/common-ssh/key.h | 16 ++++++++--------
 src/common-ssh/key.c            |  8 ++++----
 src/common-ssh/ssh.c            | 19 +++++++++----------
 3 files changed, 21 insertions(+), 22 deletions(-)

diff --git a/src/common-ssh/common-ssh/key.h b/src/common-ssh/common-ssh/key.h
index 576ba1ba..897555a3 100644
--- a/src/common-ssh/common-ssh/key.h
+++ b/src/common-ssh/common-ssh/key.h
@@ -170,7 +170,7 @@ int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
         int length, unsigned char* sig);
 
 /**
- * Verifies the fingerprint for the given hostname/port combination against
+ * Verifies the host key for the given hostname/port combination against
  * one or more known_hosts entries.  The known_host entries can either be a
  * single host_key, provided by the client, or a set of known_hosts entries
  * provided in the /etc/guacamole/ssh_known_hosts file.  Failure to correctly
@@ -178,7 +178,7 @@ int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
  * error code.  A return code of zero indiciates that either no known_hosts entries
  * were provided, or that the verification succeeded (match).  Negative values
  * indicate internal libssh2 error codes; positive values indicate a failure
- * during verification of the fingerprint against the known hosts.
+ * during verification of the host key against the known hosts.
  *
  * @param session
  *     A pointer to the LIBSSH2_SESSION structure of the SSH connection already
@@ -200,11 +200,11 @@ int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
  * @param port
  *     The port number of the server being verified.
  *
- * @param fingerprint
- *     The fingering of the server being verified.
+ * @param remote_hostkey
+ *     The host key of the remote system being verified.
  *
- * @param fp_len
- *     The length of the fingerprint being verified
+ * @param remote_hostkey_len
+ *     The length of the remote host key being verified
  *
  * @return
  *     The status of the known_hosts check.  This will be zero if no entries
@@ -213,8 +213,8 @@ int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
  *     checking.
  */
 int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* client,
-        const char* host_key, const char* hostname, int port, const char* fingerprint,
-        const size_t fp_len);
+        const char* host_key, const char* hostname, int port, const char* remote_hostkey,
+        const size_t remote_hostkey_len);
 
 #endif
 
diff --git a/src/common-ssh/key.c b/src/common-ssh/key.c
index 4d569db7..f835e4cc 100644
--- a/src/common-ssh/key.c
+++ b/src/common-ssh/key.c
@@ -247,8 +247,8 @@ int guac_common_ssh_key_sign(guac_common_ssh_key* key, const char* data,
 }
 
 int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* client,
-        const char* host_key, const char* hostname, int port, const char* fingerprint,
-        const size_t fp_len) {
+        const char* host_key, const char* hostname, int port, const char* remote_hostkey,
+        const size_t remote_hostkey_len) {
 
     LIBSSH2_KNOWNHOSTS* ssh_known_hosts = libssh2_knownhost_init(session);
     int known_hosts = 0;
@@ -296,9 +296,9 @@ int guac_common_ssh_verify_host_key(LIBSSH2_SESSION* session, guac_client* clien
     }
 
 
-    /* Check fingerprint against known hosts */
+    /* Check remote host key against known hosts */
     int kh_check = libssh2_knownhost_checkp(ssh_known_hosts, hostname, port,
-                                            fingerprint, fp_len,
+                                            remote_hostkey, remote_hostkey_len,
                                             LIBSSH2_KNOWNHOST_TYPE_PLAIN|
                                             LIBSSH2_KNOWNHOST_KEYENC_RAW,
                                             NULL);
diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 1b13520c..831245db 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -520,15 +520,14 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
         return NULL;
     }
 
-    /* Get fingerprint of host we're connecting to */
-    size_t fp_len;
-    int fp_type;
-    const char *fingerprint = libssh2_session_hostkey(session, &fp_len, &fp_type);
+    /* Get host key of remote system we're connecting to */
+    size_t remote_hostkey_len;
+    const char *remote_hostkey = libssh2_session_hostkey(session, &remote_hostkey_len, NULL);
 
-    /* Failure to generate a fingerprint means we should abort */
-    if (!fingerprint) {
+    /* Failure to retrieve a host key means we should abort */
+    if (!remote_hostkey) {
         guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-            "Failed to get fingerprint for host %s", hostname);
+            "Failed to get host key for %s", hostname);
         free(common_session);
         close(fd);
         return NULL;
@@ -536,8 +535,8 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
 
     /* SSH known host key checking. */
     int known_host_check = guac_common_ssh_verify_host_key(session, client, host_key,
-                                                           hostname, atoi(port), fingerprint,
-                                                           fp_len);
+                                                           hostname, atoi(port), remote_hostkey,
+                                                           remote_hostkey_len);
 
     /* Abort on any error codes */
     if (known_host_check != 0) {
@@ -551,7 +550,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
 
         if (known_host_check > 0)
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,
-                "Host fingerprint did not match any provided known host keys. %s", err_msg);
+                "Host key did not match any provided known host keys. %s", err_msg);
 
         free(common_session);
         close(fd);

From fe44fd7c3b57cf74c7182eb1e9538baed5d238f8 Mon Sep 17 00:00:00 2001
From: Nick Couchman <vnick@apache.org>
Date: Mon, 25 Jun 2018 20:04:09 -0400
Subject: [PATCH 20/20] GUACAMOLE-527: Remove unused error message length
 variable.

---
 src/common-ssh/ssh.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/common-ssh/ssh.c b/src/common-ssh/ssh.c
index 831245db..9dde5111 100644
--- a/src/common-ssh/ssh.c
+++ b/src/common-ssh/ssh.c
@@ -541,8 +541,7 @@ guac_common_ssh_session* guac_common_ssh_create_session(guac_client* client,
     /* Abort on any error codes */
     if (known_host_check != 0) {
         char* err_msg;
-        int err_len;
-        libssh2_session_last_error(session, &err_msg, &err_len, 0);
+        libssh2_session_last_error(session, &err_msg, NULL, 0);
 
         if (known_host_check < 0)
             guac_client_abort(client, GUAC_PROTOCOL_STATUS_SERVER_ERROR,