Chisel-Strike : A .NET XOR Encrypted Cobalt Strike Aggressor Implementation For Chisel To Utilize Faster Proxy

Chisel-Strike is a .NET XOR encrypted cobalt strike aggressor implementation for chisel to utilize faster proxy and advanced socks5 capabilities.

Why write this?

In my experience I found socks4/socks4a proxies quite slow in comparison to its socks5 counterparts and a lack of implementation of socks5 in most C2 frameworks. There is a C# wrapper around the go version of chisel called SharpChisel. This wrapper has a few issues and isn’t maintained to the latest version of chisel. It didn’t allow using shellcode with donut, reflection methods or execute-assembly. I found a fix for this using the SharpChisel-NG project.

Since the SharpChisel assembly is around 16.7 MB, execute-assembly(has a hidden size limitation of 1 MB) and similar in memory methods wouldn’t work. To maintain most of the execution in memory I incorporated the NetLoader project by Flangvik which is executed via execute-assembly to reflectively host and load a XOR encrypted version of SharpChisel with base64 arguments in memory.

As an alternative, it is also possible to implement similar C# proxies like SharpSocks by replacing the appropriate chisel binaries in the project.

Setup

Note: If using a Windows teamserver skip steps 2 and 3.

• Clone/download the repository: git clone https://github.com/m3rcer/Chisel-Strike.git
• Make all binaries executable:

• cd Chisel-Strike
• chmod +x -R chisel-modules
• chmod +x -R tools

• Install Mingw-w64 and mono:

• sudo apt-get install mingw-w64
• sudo apt install mono-complete

• Import ChiselStrike.cna in cobalt strike using the Script Manager

Recompile binaries from the src folder if needed.

Usage

chisel can be executed on both the teamserver (windows/linux) and the beacon. With either acting as the server/client. A normal execution flow would be to setup a chisel server on the teamserver and create a client on the beacon connecting back to the teamserver.

Commands

• chisel <client/server> <command>: Run Chisel on a beacon
• chisel-tms <client/server> <command>: Run Chisel on your teamserver
• chisel-enc: XOR Encrypt SharpChisel.exe with a password of choice
• chisel-jobs: List active chisel jobs on the teamserver and beacon
• chisel-kill: Kill active chisel jobs on a beacon
• chisel-tms-kill: Kill active chisel jobs on teamserver

Example

OPSEC

NetLoader can easily be obfuscated and used to bypass defender using projects like NimCrypt2 and the like.

Yet SharpChisel.exe drops a dll on disk due to the use of Costura/Fody packages at a location similar to: C:\Users\m3rcer\AppData\Local\Temp\Costura\CB9433C24E75EC539BF34CD1AA12B236\64\main.dll which is detected by defender. It is advised to obfuscate chisel dll’s using projects like gobfuscate in the SharpChisel-NG project and re-build new SharpChisel-NG binaries as shown here.