Nimcrypt2 : .NET, PE, And Raw Shellcode Packer/Loader Written In Nim

Nimcrypt2 is yet another PE packer/loader designed to bypass AV/EDR. It is an improvement on my original Nimcrypt project, with the main improvements being the use of direct syscalls and the ability to load regular PE files as well as raw shellcode.

Before going any further, I must acknowledge those who did the VAST majority of work and research that this project depends on. Firstly, I must thank @byt3bl33d3r for his Offensive Nim repo, and @ShitSecure for all of the code snippets he’s publicly released. That is what the original version of this tool was created from, and the current version is no different. Particularly, the new PE loading functionality used in this tool is just an implementation of ShitSecure’s recently released Nim-RunPE code. As of 3/14/22, this code also uses his GetSyscallStub code for dynamic syscall usage. I highly encourage sponsoring him for access to his own Nim PE Packer, which is no doubt a much better and more featureful version of this.

Additionally, I would like to thank @ajpc500 for his NimlineWhispers2 project that this tool uses for direct syscalls. I cannot stress enough how this project is simply an amalgamation of the public work of those previously mentioned, so all credit must go to them.

Nimcrypt v 2.0
Usage:
nimcrypt -f file_to_load -t csharp/raw/pe [-o ] [-p ] [-n] [-u] [-s] [-e] [-g] [-l] [-v]
nimcrypt (-h | –help)
Options:
-h –help Show this screen.
–version Show version.
-f –file filename File to load
-t –type filetype Type of file (csharp, raw, or pe)
-p –process process Name of process for shellcode injection
-o –output filename Filename for compiled exe
-u –unhook Unhook ntdll.dll
-v –verbose Enable verbose messages during execution
-e –encrypt-strings Encrypt strings using the strenc module
-g –get-syscallstub Use GetSyscallStub instead of NimlineWhispers2
-l –llvm-obfuscator Use Obfuscator-LLVM to compile binary
-n –no-randomization Disable syscall name randomization
-s –no-sandbox Disable sandbox checks

Features

• NtQueueApcThread Shellcode Execution w/ PPID Spoofing & 3rd Party DLL Blocking
• NimlineWhispers2 & GetSyscallStub for Syscall Use
• Syscall Name Randomization
• Ability to load .NET and Regular PE Files
• AES Encryption with Dynamic Key Generation
• LLVM-Obfuscator Compatibility
• String Encryption
• Sandbox Evasion

Tested and Confirmed Working on

• Windows 11 (10.0.22000)
• Windows 10 21H2 (10.0.19044)
• Windows 10 21H1 (10.0.19043)
• Windows 10 20H2 (10.0.19042)
• Windows 10 19H2 (10.0.18363)
• Windows Server 2019 (10.0.17763)

Installation/Dependencies

Nimcrypt2 is designed to be used on Linux systems with Nim installed. Before installing Nim, you must ensure that you have the following packages installed via your package manager:

sudo apt install gcc mingw-w64 xz-utils git

To install Nim, I prefer to use choosenim as follows:

curl https://nim-lang.org/choosenim/init.sh -sSf | sh
echo “export PATH=$HOME/.nimble/bin:$PATH” >> ~/.bashrc
export PATH=$HOME/.nimble/bin:$PATH

Nimcrypt2 also depends on a few packages that can be installed via Nimble. This can be done like so:

nimble install winim nimcrypto docopt ptr_math strenc

With all the dependencies now installed, Nimcrypt2 can be compiled like so:

nim c -d=release –cc:gcc –embedsrc=on –hints=on –app=console –cpu=amd64 –out=nimcrypt nimcrypt.nim

OPTIONAL: To use the Obfuscator-LLVM flag, you must have it installed on your system alongside wclang. I’ve found this to be a bit of a pain but you should be able to do it with a little perseverance. Here’s a quick step-by-step that worked on my Kali Linux system:

• Clone desired version of Obfuscator-LLVM and build it
• Once compiled, backup the existing version of clang and move the new Obfuscator-LLVM version of clang to /usr/bin/
• Install wclang and add it’s binaries to your PATH
• Backup existing clang library files, copy new newly built Obfuscator-LLVM library includes to /usr/lib/clang/OLD_VERSION/

In addition, you must add the following lines to your nim.cfg file to point nim to your wclang binaries:

amd64.windows.clang.exe = “x86_64-w64-mingw32-clang”
amd64.windows.clang.linkerexe = “x86_64-w64-mingw32-clang”
amd64.windows.clang.cpp.exe = “x86_64-w64-mingw32-clang++”
amd64.windows.clang.cpp.linkerexe = “x86_64-w64-mingw32-clang++”

amd64.windows.clang.cpp.linkerexe = "x86_64-w64-mingw32-clang++"

There is probably a better way to do this but this is what worked for me. If you have issues, just keep trying and ensure that you can run x86_64-w64-mingw32-clang -v and it shows “Obfuscator-LLVM” in the output. Also ensure MinGW is using the Obfuscator-LLVM library files: Nim will give you an error if not.