Browser Pivot for Chrome

Hey all,

Today’s post is about Browser Pivoting with Chrome. For anyone unaware of Browser Pivoting, it’s a technique which essentially leverages an exploited system to gain access to the browser’s authenticated sessions. This is not a new technique, in fact, Raphael Mudge wrote about it in 2013.┬áDetailed in the linked post, the Browser Pivot module for Cobalt Strike targets IE only, and as far as I know, cannot be used against Chrome. In this post we’re trying to achieve a similar result while taking a different approach – stealing the target’s Chrome profile in real time. Just a FYI, if you have the option to use Cobalt Strike’s Browser Pivot module instead, do so, it’s much cleaner.

You might be thinking – “why go through the trouble?” If I’ve exploited the system I can mimikatz or keylog to get the target’s credentials and by extension, the resources they have access to. Well, one major application that comes to mind is multi-factor authentication (MFA). Organizations are catching on that a single password alone is not nearly sufficient in protecting valued network resources, which is fantastic news! Personally, I have the opportunity to do offensive engagements on OT targets which often have multiple tiers of authentication and networking; it’s my generalization that MFA-less sites tend to fall much quicker than MFA sites – hours or days vs weeks or not at all, respectively. In my opinion, MFA at a security boundary is one of the most important security controls one can implement.

You also might be thinking – “here you are touting the potency of MFA, yet you are talking about hijacking MFA sessions”. Again, this technique has been around since 2013 and the specific code developed for this PoC is all publicly accessible. Advanced adversaries have access to and are most likely employing this technique. Our offensive engagements need to emulate these threats because that’s how we get better from a defensive standpoint – steel sharpens steel.

How To Defend

First off, if you’ve forced an attacker to go beyond traditional credential theft to gain access to critical network resources, congratulations! This walkthrough has quite a few (loud) indicators that can point to malicious activity. We’re starting and stopping services, modifying system32 files, modifying registry, creating and deleting VSS snapshots, and ending it with a remote desktop session to the target. All this activity can easily be detected.

What Does It Do?

High level, this PoC attempts to do the following:

  1. Modify the system to allow multiple Remote Desktop connections and remove RemoteApp restrictions.
  2. Using VSS, copy the target’s in-use Chrome profile to another file folder.
  3. Using RemoteApp and proxychains, remotely open a Chrome instance pointing to that copied profile path.
    • If you prefer, I think the profile could be copied over to the attacking VM and leveraged using proxychains and chromium. That being said, I would imagine this type of technique is time sensitive.

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