hacktricks/src/network-services-pentesting/pentesting-kerberos-88/README.md

88tcp/udp - Pentesting Kerberos

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Basic Information

Kerberos operates on a principle where it authenticates users without directly managing their access to resources. This is an important distinction because it underlines the protocol's role in security frameworks.

In environments like Active Directory, Kerberos is instrumental in establishing the identity of users by validating their secret passwords. This process ensures that each user's identity is confirmed before they interact with network resources. However, Kerberos does not extend its functionality to evaluate or enforce the permissions a user has over specific resources or services. Instead, it provides a secure way of authenticating users, which is a critical first step in the security process.

After authentication by Kerberos, the decision-making process regarding access to resources is delegated to individual services within the network. These services are then responsible for evaluating the authenticated user's rights and permissions, based on the information provided by Kerberos about the user's privileges. This design allows for a separation of concerns between authenticating the identity of users and managing their access rights, enabling a more flexible and secure approach to resource management in distributed networks.

Default Port: 88/tcp/udp

PORT   STATE SERVICE
88/tcp open  kerberos-sec

To learn how to abuse Kerberos you should read the post about Active Directory.

Kerberos-only environments: client prep and troubleshooting

When NTLM is disabled on domain services (SMB/WinRM/etc.), you must authenticate with Kerberos. Common pitfalls and a working workflow:

• Time synchronization is mandatory. If your host clock is skewed by more than a few minutes you will see KRB_AP_ERR_SKEW and all Kerberos auth will fail. Sync against the DC:

# quick one-shot sync (requires sudo)
sudo ntpdate <dc.fqdn> || sudo chronyd -q 'server <dc.fqdn> iburst'

• Generate a valid krb5.conf for the target realm/domain. netexec (CME fork) can output one for you while testing SMB:

# Generate krb5.conf and install it
netexec smb <dc.fqdn> -u <user> -p '<pass>' -k --generate-krb5-file krb5.conf
sudo cp krb5.conf /etc/krb5.conf

• Obtain a TGT and verify the ccache:

kinit <user>
klist

• Use Kerberos with SMB tooling (no passwords sent, uses your ccache):

# netexec / CME
netexec smb <dc.fqdn> -k            # lists shares, runs modules using Kerberos
# impacket examples also support -k / --no-pass to use the ccache
smbclient --kerberos //<dc.fqdn>/IPC$

• GSSAPI SSH single sign-on (OpenSSH to Windows OpenSSH server):

# Ensure krb5.conf is correct and you have a TGT (kinit)
# Use the FQDN that matches the host SPN. Wrong names cause: "Server not found in Kerberos database"
ssh -o GSSAPIAuthentication=yes <user>@<host.fqdn>

Tips:

• Ensure your /etc/hosts resolves the exact FQDN you will SSH/SMB to, and that it comes before any bare domain entries if you are overriding DNS. SPN mismatches break GSSAPI.
• If NTLM is disabled on SMB you may see STATUS_NOT_SUPPORTED with NTLM attempts; add -k to force Kerberos.

More

Shodan

• port:88 kerberos

MS14-068

The MS14-068 flaw permits an attacker to tamper with a legitimate user's Kerberos login token to falsely claim elevated privileges, such as being a Domain Admin. This counterfeit claim is mistakenly validated by the Domain Controller, enabling unauthorized access to network resources across the Active Directory forest.

{{#ref}} https://adsecurity.org/?p=541 {{#endref}}

Other exploits: https://github.com/SecWiki/windows-kernel-exploits/tree/master/MS14-068/pykek

References

• NetExec (CME) wiki – Kerberos and krb5.conf generation
• OpenSSH GSSAPIAuthentication
• MIT Kerberos – Using Kerberos on UNIX
• 0xdf – HTB: TheFrizz

HackTricks Automatic Commands

Protocol_Name: Kerberos    #Protocol Abbreviation if there is one.
Port_Number:  88   #Comma separated if there is more than one.
Protocol_Description: AD Domain Authentication         #Protocol Abbreviation Spelled out

Entry_1:
  Name: Notes
  Description: Notes for Kerberos
  Note: |
    Kerberos operates on a principle where it authenticates users without directly managing their access to resources. This is an important distinction because it underlines the protocol's role in security frameworks.
    In environments like **Active Directory**, Kerberos is instrumental in establishing the identity of users by validating their secret passwords. This process ensures that each user's identity is confirmed before they interact with network resources. However, Kerberos does not extend its functionality to evaluate or enforce the permissions a user has over specific resources or services. Instead, it provides a secure way of authenticating users, which is a critical first step in the security process.

    https://book.hacktricks.wiki/en/network-services-pentesting/pentesting-kerberos-88/index.html

Entry_2:
  Name: Pre-Creds
  Description: Brute Force to get Usernames
  Command: nmap -p 88 --script=krb5-enum-users --script-args krb5-enum-users.realm="{Domain_Name}",userdb={Big_Userlist} {IP}

Entry_3:
  Name: With Usernames
  Description: Brute Force with Usernames and Passwords
  Note: consider git clone https://github.com/ropnop/kerbrute.git ./kerbrute -h

Entry_4:
  Name: With Creds
  Description: Attempt to get a list of user service principal names
  Command: GetUserSPNs.py -request -dc-ip {IP} active.htb/svc_tgs

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