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Pass-the-Golden-Ticket with Cobalt Strike’s Beacon

July 30, 2014

Back in May, I wrote up some impressions about Meterpreter’s Kiwi extension. It’s Mimikatz 2.0, complete with its ability to generate a Kerberos “Golden Ticket” with domain-admin rights offline.

I’ve had a very positive experience with this capability since May. My best practice is to create a Golden Ticket catalog. When you capture a domain controller, get the krbtgt hash, and store it in this catalog. Keep this catalog for the duration of the engagement.

Golden Ticket Catalog

= Network Name =
1. DOMAIN NAME
2. Domain Administrator User
3. DOMAIN SID
4. krbtgt hash

If someone cleans you out of their systems: just phish another user, use the catalog information to generate a ticket, apply the ticket, and you’re right back at domain admin. It’s nice. The Golden Ticket capability really is a “persistent” attacker’s dream.

This assumes that the network owners don’t follow steps to re-roll the krbtgt user’s password. I suspect this will become part of a post-attack cleanup process, but it’ll take time for this practice to disseminate.

I recommend that you keep a catalog of ticket information over a collection of pre-made tickets. Here’s why: You may create a ticket for a user. If that account gets disabled, the ticket will no longer work. If you end up in this situation–use the net group command to query for the new domain admins and update your catalog accordingly.

To apply a self-generated Kerberos ticket to my current session: I have to either drop something to disk (mimikatz 2.0) or I have to switch to interactive command and control with Meterpreter. Those who’ve worked with me know that I dislike interactive C2. It has its place, but it’s also an opportunity to attract attention from a good network defense team. I’m also not a fan of touching disk–unless I really have to.

So, what does a hacker do when caught between two unlikeable choices? Make a third.

I’ve added support for self-generated Kerberos tickets to Cobalt Strike’s Beacon. Now, you may inject a Golden Ticket into a Beacon session and use it for lateral movement. This is a natural marriage.

Beacon’s lateral movement workflow requires its user to generate an artifact, copy it to a target host, and schedule it to run. I’ve built a minimal set of tools into Beacon (e.g., privilege escalation, token stealing, and now ticket injection) to support this. The rest of these steps happen using native tools on the target’s system. I’m a big fan of doing lateral movement with native tools as it’s less likely to look like hacker activity.

Seriously, if I have to answer for one more service named XtAx754A running a malicious ApacheBench–I’m going to scream!

Here’s a video that shows pass-the-ticket with Cobalt Strike’s Beacon:

If you’re headed to Las Vegas for BlackHat USA or DEF CON–you have an opportunity to hear more on Kerberos abuse at both conferences. Benjamin Delpy and Alva “Skip” Duckwall will deliver Abusing Microsoft Kerberos: Sorry You Guys Don’t Get It at BlackHat USA. Chris Campbell will deliver The Secret Life of KRBTGT at DEF CON. I expect that these talks will give this subject the authoritative treatment and depth it deserves. Be sure to check them out.

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