COM Hijacking for Lateral Movement

Hey all,

This post is about leveraging COM hijacking for lateral movement. I’m going to stay away from deep-diving COM internals as hijacking is not a new topic and has been explored by people far smarter than I, check out the references for awesome COM material. Instead, I’ll be taking a look at how tinkering with the registry and calling a COM object remotely (DCOM) can provide lateral movement options.

As a humble net-pen guy, I have to admit I haven’t encountered a target which monitors HKLM\..\CLSID, so I wanted to develop a tool which could explain the importance of doing so. Also, from an offsec standpoint, I like this approach as it provides the ability to live inside a legitimate process without dropping an executable to disk or using one of the “usual suspects” executables to kick off my session. However, there are two risks with using this type of approach: the modifications to the remote registry are clearly malicious and can leave a system in an non-operational state.

Furthermore, there are a ton of interesting use cases when tinkering with the AppID registry key as well. For example, setting RunAs to a different value might kick off our C2 session to a context of our choosing (Interactive User or SYSTEM). I’m hoping to explore this in future posts.

References

DCOM_Work

In-line with any proof-of-concept coding I do, **use at your own risk**. I do this type of after-hours work to further understand a topic and just become a better coder (I’m not good). Any program which tinkers with the registry can seriously break a system, so you’ve been warned.

DCOM_Work does everything possible to revert the registry configuration and permissions, but if the application terminates unexpectedly you might be left with a hung registry value which will impact system operation. In the link below, I’ve also included DCOM_Revert which will try to revert the target registry configuration. However, it wouldn’t hurt to have regedit.exe + remote registry on standby to modify the value if need be.

 

The operational comments of DCOM_Work are pretty self-explanatory; however, there are a few additional comments I would like to make.

  1. The mmgaserver module can be touch and go depending on the target OS, especially Server OSes, I’ve had pretty constant success using the Wordpad module. Coming up with new processes to inject into is pretty trivial though.
  2. The temp share is configured to permit null share sessions and ANONYMOUS LOGON to host the landing DLL which will be injected into wordpad.exe or mmgaserver.exe. To bypass this requirement, the RunAs registry value in the associated AppID registry key could be set to Interactive User; however, this would introduce a requirement of an active session on the remote target.
  3. The landing DLL used in the video was a stripped down version of COMProxy by Leoloobeek. From my experience, calling the intended COM DLL (wordpad -> uiribbon.dll or mmgaserver -> Windows.State.RepositoryPS.dll) provides a more stable injected process.
  4. To kick off the DCOM instance, powershell is spawned via CreateProcess which might get flagged by certain security products. There are better ways to approach this but not right now.
  5. The following changes will occur remotely on a default Windows 10 system.
    1. If the remote registry is disabled and stopped, it will be set to manual_start and started.
    2. If the connecting account does not have write access to the target registry key, the built-in administrators group will be made owner and provided write-access.
    3. The target value will be changed to the specified DLL path provided in the program arguments – (\\192.168.1.10\temp\GetClassObjectDLL_WordPad.dll).
  6. If everything works, the following reversions will be performed after the DCOM instance is created.
    1. The target value will be reverted to the starting DLL path obtained during the initial gathering phase of execution (%systemroot%\system32\uiribbon.dll).
    2. If the registry permissions were changed, the registry key will be reverted to the original owner (including TrustedInstaller) and the built-in administrators permissions will be set to KEY_READ, the default on Windows 10.
    3. If the remote registry settings were changed, it will be reverted to it’s initial start state (disabled, manual_start, auto_start).

DCOM_Work Link

On the Defensive

COM Hijacking is actively employed by adversaries so it’s important to prevent and detect; fortunately for us, this is easy to detect. Employing sysmon with a configuration like SwiftOnSecurity’s example here will do the trick. As we can see in the details, this will never happen during normal operation and is easy to distinguish as malicious. However, it’s important to note that there are quite a few weird and wonderful registry keys under \..\CLSID\{GUID}\, some of which I’m sure could hijack execution, so it’s best to keep dynamic with sysmon configurations.

<TargetObject name="T1122" condition="end with">\InprocServer32\(Default)</TargetObject>

1

From a prevention standpoint, this is a bit more tricky but definitely doable. In my home lab the target remote system was running up-to-date Defender which highlights standard AV probably won’t do much (MS or whatever). Applocker DLL rules could restrict UNC paths quite simply, but this is more a band-aid … and honestly, who isn’t driven away by that ominous DLL rules can cause performance issues message. Ultimately, my hope was to have WDAC setup in my home lab but I couldn’t get it done in time. From my understanding, WDAC could have blocked this type of activity. I’m hoping to perform active testing in my lab and come up with a conclusive answer at a later date.

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