Kerbrute
Kerbrute
A tool to quickly bruteforce and enumerate valid Active Directory accounts through Kerberos Pre-Authentication
Grab the latest binaries from the releases page to get started.
Background
This tool grew out of some bash scripts I wrote a few years ago to perform bruteforcing using the Heimdal Kerberos client from Linux. I wanted something that didn't require privileges to install a Kerberos client, and when I found the amazing pure Go implementation of Kerberos gokrb5, I decided to finally learn Go and write this.
Bruteforcing Windows passwords with Kerberos is much faster than any other approach I know of, and potentially stealthier since pre-authentication failures do not trigger that "traditional" An account failed to log on event 4625. With Kerberos, you can validate a username or test a login by only sending one UDP frame to the KDC (Domain Controller)
For more background and information, check out my Troopers 2019 talk, Fun with LDAP and Kerberos (link TBD)
Usage
Kerbrute has three main commands:
bruteuser - Bruteforce a single user's password from a wordlist
bruteforce - Read username:password combos from a file or stdin and test them
passwordspray - Test a single password against a list of users
userenum - Enumerate valid domain usernames via Kerberos
A domain (-d) or a domain controller (--dc) must be specified. If a Domain Controller is not given the KDC will be looked up via DNS.
By default, Kerbrute is multithreaded and uses 10 threads. This can be changed with the -t option.
Output is logged to stdout, but a log file can be specified with -o.
By default, failures are not logged, but that can be changed with -v.
Lastly, Kerbrute has a --safe option. When this option is enabled, if an account comes back as locked out, it will abort all threads to stop locking out any other accounts.
The help command can be used for more information
User Enumeration
To enumerate usernames, Kerbrute sends TGT requests with no pre-authentication. If the KDC responds with a PRINCIPAL UNKNOWN error, the username does not exist. However, if the KDC prompts for pre-authentication, we know the username exists and we move on. This does not cause any login failures so it will not lock out any accounts. This generates a Windows event ID 4768 if Kerberos logging is enabled.
Password Spray
With passwordspray, Kerbrute will perform a horizontal brute force attack against a list of domain users. This is useful for testing one or two common passwords when you have a large list of users. WARNING: this does will increment the failed login count and lock out accounts. This will generate both event IDs 4768 - A Kerberos authentication ticket (TGT) was requested and 4771 - Kerberos pre-authentication failed
Brute User
This is a traditional bruteforce account against a username. Only run this if you are sure there is no lockout policy! This will generate both event IDs 4768 - A Kerberos authentication ticket (TGT) was requested and 4771 - Kerberos pre-authentication failed
Brute Force
This mode simply reads username and password combinations (in the format username:password) from a file or from stdin and tests them with Kerberos PreAuthentication. It will skip any blank lines or lines with blank usernames/passwords. This will generate both event IDs 4768 - A Kerberos authentication ticket (TGT) was requested and 4771 - Kerberos pre-authentication failed
Installing
You can download pre-compiled binaries for Linux, Windows and Mac from the releases page. If you want to live on the edge, you can also install with Go:
With the repository cloned, you can also use the Make file to compile for common architectures:
Credits
Huge shoutout to jcmturner for his pure Go implementation of KRB5: https://github.com/jcmturner/gokrb5 . An amazing project and very well documented. Couldn't have done any of this without that project.
Shoutout to audibleblink for the suggestion and implementation of the delay option!
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