OffensiveNim
My experiments in weaponizing Nim for implant development and general offensive operations.
Table of Contents
- OffensiveNim
- Why Nim?
- Examples in this repo
- Compiling the examples
- Cross Compiling
- Interfacing with C/C++
- Creating Windows DLLs with an exported DllMain
- Optimizing executables for size
- Reflectively Loading Nim Executables
- Executable size difference with the Winim Library
- Opsec Considirations
- Converting C Code to Nim
- Language Bridges
- Debugging
- Setting up a dev environment
- Pitfalls I found myself falling into
- Interesting Nim Libraries
- Nim for Implant Dev Links
- Contributors
Why Nim?
- Compiles directly to C, C++, Objective-C and Javascript.
- Since it doesn't rely on a VM/runtime does not produce what I like to call "T H I C C malwarez" as supposed to other languages (e.g. Golang)
- Python inspired syntax, allows rapid native payload creation & prototyping.
- Has extremely mature FFI (Foreign Function Interface) capabilities.
- Avoids making you actually write in C/C++ and subsequently avoids introducing a lot of security issues into your software.
- Super easy cross compilation to Windows from *nix/MacOS, only requires you to install the
mingw
toolchain and passing a single flag to the nim compiler. - The Nim compiler and the generated executables support all major platforms like Windows, Linux, BSD and macOS. Can even compile to Nintendo switch , IOS & Android. See the cross-compilation section in the Nim compiler usage guide
- You could technically write your implant and c2 backend both in Nim as you can compile your code directly to Javascript. Even has some initial support for WebAssembly's
Examples in this repo that work
File | Description |
---|---|
pop_bin.nim | Call MessageBox WinApi without using the Winim library |
pop_winim_bin.nim | Call MessageBox with the Winim libary |
pop_winim_lib.nim | Example of creating a Windows DLL with an exported DllMain |
execute_assembly_bin.nim | Hosts the CLR, reflectively executes .NET assemblies from memory |
clr_host_cpp_embed_bin.nim | Hosts the CLR by directly embedding C++ code, executes a .NET assembly from disk |
scshell_c_embed_bin.nim | Shows how to quickly weaponize existing C code by embedding SCShell (C) directly within Nim |
fltmc_bin.nim | Enumerates all Minifilter drivers |
blockdlls_acg_ppid_spoof_bin.nim | Creates a suspended process that spoofs its PPID to explorer.exe, also enables BlockDLLs and ACG |
named_pipe_client_bin.nim | Named Pipe Client |
named_pipe_server_bin.nim | Named Pipe Server |
embed_rsrc_bin.nim | Embeds a resource (zip file) at compile time and extracts contents at runtime |
self_delete_bin.nim | A way to delete a locked or current running executable on disk. Method discovered by @jonasLyk |
encrypt_decrypt_bin.nim | Encryption/Decryption using AES256 (CTR Mode) using the Nimcrypto library |
amsi_patch_bin.nim | Patches AMSI out of the current process |
amsi_providerpatch_bin.nim | Patches the AMSI Provider DLL (in this case MpOav.dll) to bypass AMSI. Published here |
etw_patch_bin.nim | Patches ETW out of the current process (Contributed by ) |
wmiquery_bin.nim | Queries running processes and installed AVs using using WMI |
out_compressed_dll_bin.nim | Compresses, Base-64 encodes and outputs PowerShell code to load a managed dll in memory. Port of the orignal PowerSploit script to Nim. |
dynamic_shellcode_local_inject_bin.nim | POC to locally inject shellcode recovered dynamically instead of hardcoding it in an array. |
shellcode_callback_bin.nim | Executes shellcode using Callback functions |
shellcode_bin.nim | Creates a suspended process and injects shellcode with VirtualAllocEx /CreateRemoteThread . Also demonstrates the usage of compile time definitions to detect arch, os etc.. |
shellcode_fiber.nim | Shellcode execution via fibers |
shellcode_inline_asm_bin.nim | Executes shellcode using inline assembly |
syscalls_bin.nim | Shows how to make direct system calls |
execute_powershell_bin.nim | Hosts the CLR & executes PowerShell through an un-managed runspace |
passfilter_lib.nim | Log password changes to a file by (ab)using a password complexity filter |
minidump_bin.nim | Creates a memory dump of lsass using MiniDumpWriteDump |
http_request_bin.nim | Demonstrates a couple of ways of making HTTP requests |
execute_sct_bin.nim | .sct file Execution via GetObject() |
scriptcontrol_bin.nim | Dynamically execute VBScript and JScript using the MSScriptControl COM object |
excel_com_bin.nim | Injects shellcode using the Excel COM object and Macros |
keylogger_bin.nim | Keylogger using SetWindowsHookEx |
memfd_python_interpreter_bin.nim | Use memfd_create syscall to load a binary into an anonymous file and execute it with execve syscall. |
uuid_exec_bin.nim | Plants shellcode from UUID array into heap space and uses EnumSystemLocalesA Callback in order to execute the shellcode. |
unhookc.nim | Unhooks ntdll.dll to evade EDR/AV hooks (embeds the C code template from ired.team) |
unhook.nim | Unhooks ntdll.dll to evade EDR/AV hooks (pure nim implementation) |
taskbar_ewmi_bin.nim | Uses Extra Window Memory Injection via Running Application property of TaskBar in order to execute the shellcode. |
fork_dump_bin.nim | (ab)uses Window's implementation of fork() and acquires a handle to a remote process using the PROCESS_CREATE_PROCESS access right. It then attempts to dump the forked processes memory using MiniDumpWriteDump() |
ldap_query_bin.nim | Perform LDAP queries via COM by using ADO's ADSI provider |
sandbox_process_bin.nim | This sandboxes a process by setting it's integrity level to Untrusted and strips important tokens. This can be used to "silently disable" a PPL process (e.g. AV/EDR) |
list_remote_shares.nim | Use NetShareEnum to list the share accessible by the current user |
chrome_dump_bin.nim | Read and decrypt cookies from Chrome's sqlite database |
suspended_thread_injection.nim | Shellcode execution via suspended thread injection |
dns_exfiltrate.nim | Simple DNS exfiltration via TXT record queries |
Examples that are a WIP
File | Description |
---|---|
amsi_patch_2_bin.nim | Patches AMSI out of the current process using a different method (WIP, help appreciated) |
excel_4_com_bin.nim | Injects shellcode using the Excel COM object and Excel 4 Macros (WIP) |
Compiling the examples in this repo
This repository does not provide binaries, you're gonna have to compile them yourself. This repo was setup to cross-compile the example Nim source files to Windows from Linux or MacOS.
Easy Way (Recommended)
Use VSCode Devcontainers to automatically setup a development environment for you (See the Setting Up a Dev Environment section). Once that's done simply run make
.
Hard way (For the bold)
Install Nim using your systems package manager (for Windows use the installer on the official website)
brew install nim
apt install nim
choco install nim
(Nim also provides a docker image on Dockerhub)
You should now have the nim
& nimble
commands available, the former is the Nim compiler and the latter is Nim's package manager.
Install the Mingw
toolchain needed for cross-compilation to Windows (Not needed if you're compiling on Windows):
- *nix:
apt-get install mingw-w64
- MacOS:
brew install mingw-w64
Finally, install the magnificent Winim library, along with zippy and nimcrypto
nimble install winim zippy nimcrypto
Then cd into the root of this repository and run make
.
You should find the binaries and dlls in the bin/
directory
Cross Compiling
See the cross-compilation section in the Nim compiler usage guide, for a lot more details.
Cross compiling to Windows from MacOs/*nix requires the mingw
toolchain, usually a matter of just brew install mingw-w64
or apt install mingw-w64
.
You then just have to pass the -d=mingw
flag to the nim compiler.
E.g. nim c -d=mingw --app=console --cpu=amd64 source.nim
Interfacing with C/C++
See the insane FFI section in the Nim manual.
If you're familiar with csharps P/Invoke it's essentially the same concept albeit a looks a tad bit uglier:
Calling MessageBox
example
type
HANDLE* = int
HWND* = HANDLE
UINT* = int32
LPCSTR* = cstring
proc MessageBox*(hWnd: HWND, lpText: LPCSTR, lpCaption: LPCSTR, uType: UINT): int32
{.discardable, stdcall, dynlib: "user32", importc: "MessageBoxA".}
MessageBox(0, "Hello, world !", "Nim is Powerful", 0)
For any complex Windows API calls use the Winim library, saves an insane amount of time and doesn't add too much to the executable size (see below) depending on how you import it.
Even has COM support!!!
DllMain
Creating Windows DLLs with an exported Big thanks to the person who posted this on the Nim forum.
The Nim compiler tries to create a DllMain
function for you automatically at compile time whenever you tell it to create a windows DLL, however, it doesn't actually export it for some reason. In order to have an exported DllMain
you need to pass --nomain
and define a DllMain
function yourself with the appropriate pragmas (stdcall, exportc, dynlib
).
You need to also call NimMain
from your DllMain
to initialize Nim's garbage collector. (Very important, otherwise your computer will literally explode).
Example:
import winim/lean
proc NimMain() {.cdecl, importc.}
proc DllMain(hinstDLL: HINSTANCE, fdwReason: DWORD, lpvReserved: LPVOID) : BOOL {.stdcall, exportc, dynlib.} =
NimMain()
if fdwReason == DLL_PROCESS_ATTACH:
MessageBox(0, "Hello, world !", "Nim is Powerful", 0)
return true
To compile:
nim c -d=mingw --app=lib --nomain --cpu=amd64 mynim.dll
Creating XLLs
You can make an XLL (an Excel DLL, imagine that) with an auto open function that can be used for payload delivery. The following code creates a simple for an XLL that has an auto open function and all other boilerplate code needed to compile as a link library. The POC compiles as a DLL, you can then change the extension to .xll and it will open in Excel and run the payload when double clicked:
#[
Compile:
nim c -d=mingw --app=lib --nomain --cpu=amd64 nim_xll.nim
Will compile as a DLL, you can then just change the extension to .xll
]#
import winim/lean
proc xlAutoOpen() {.stdcall, exportc, dynlib.} =
MessageBox(0, "Hello, world !", "Nim is Powerful", 0)
proc NimMain() {.cdecl, importc.}
proc DllMain(hinstDLL: HINSTANCE, fdwReason: DWORD, lpvReserved: LPVOID) : BOOL {.stdcall, exportc, dynlib.} =
NimMain()
return true
There are many other sneaky things that can be done with XLLs. See more examples of XLL tradecraft here.
Optimizing executables for size
Taken from the Nim's FAQ page
For the biggest size decrease use the following flags -d:danger -d:strip --opt:size
Additionally, I've found you can squeeze a few more bytes out by passing --passc=-flto --passl=-flto
to the compiler. Also take a look at the Makefile
in this repo.
These flags decrease sizes dramatically: the shellcode injection example goes from 484.3 KB to 46.5 KB when cross-compiled from MacOSX!
Reflectively Loading Nim Executables
Huge thanks to @Shitsecure for figuring this out!
By default, Nim doesn't generate PE's with a relocation table which is needed by most tools that reflectively load EXE's.
To generate a Nim executable with a relocation section you need to pass a few additional flags to the linker.
Specifically: --passL:-Wl,--dynamicbase
Full example command:
nim c --passL:-Wl,--dynamicbase my_awesome_malwarez.nim
Executable size difference when using the Winim library vs without
Incredibly enough the size difference is pretty negligible. Especially when you apply the size optimizations outlined above.
The two examples pop_bin.nim
and pop_winim_bin.nim
were created for this purpose.
The former defines the MessageBox
WinAPI call manually and the latter uses the Winim library (specifically winim/lean
which is only the core SDK, see here), results:
byt3bl33d3r@ecl1ps3 OffensiveNim % ls -lah bin
-rwxr-xr-x 1 byt3bl33d3r 25K Nov 20 18:32 pop_bin_32.exe
-rwxr-xr-x 1 byt3bl33d3r 32K Nov 20 18:32 pop_bin_64.exe
-rwxr-xr-x 1 byt3bl33d3r 26K Nov 20 18:33 pop_winim_bin_32.exe
-rwxr-xr-x 1 byt3bl33d3r 34K Nov 20 18:32 pop_winim_bin_64.exe
If you import the entire Winim library with import winim/com
it adds only around ~20ish KB which considering the amount of functionality it abstracts is 100% worth that extra size:
byt3bl33d3r@ecl1ps3 OffensiveNim % ls -lah bin
-rwxr-xr-x 1 byt3bl33d3r 42K Nov 20 19:20 pop_winim_bin_32.exe
-rwxr-xr-x 1 byt3bl33d3r 53K Nov 20 19:20 pop_winim_bin_64.exe
Opsec Considerations
Because of how Nim resolves DLLs dynamically using LoadLibrary
using it's FFI none of your external imported functions will actually show up in the executables static imports (see this blog post for more on this):
If you compile Nim source to a DLL, seems like you'll always have an exported NimMain
, no matter if you specify your own DllMain
or not (??). This could potentially be used as a signature, don't know how many shops are actually using Nim in their development stack. Definitely stands out.
Converting C code to Nim
https://github.com/nim-lang/c2nim
Used it to translate a bunch of small C snippets, haven't tried anything major.
Language Bridges
-
Python integration https://github.com/yglukhov/nimpy
- This is actually super interesting, especially this part. With some modification could this load the PythonxXX.dll from memory?
-
Jave VM integration: https://github.com/yglukhov/jnim
Debugging
Use the repr()
function in combination with echo
, supports almost all (??) data types, even structs!
Setting up a dev environment
This repository supports VSCode Devcontainers which allows you to develop in a Docker container. This automates setting up a development environment for you.
- Install VSCode and Docker desktop
- Clone this repo and open it in VSCode
- Install the
Visual Studio Code Remote - Containers
extension - Open the command pallete and select
Remote-Containers: Reopen in Container
command
VScode will now build the Docker image (will take a bit) and put you right into your pre-built Nim dev environment!
Pitfalls I found myself falling into
-
When calling winapi's with Winim and trying to pass a null value, make sure you pass the
NULL
value (defined within the Winim library) as supposed Nim's builtinnil
value. (Ugh) -
To get the OS handle to the created file after calling
open()
on Windows, you need to callf.getOsFileHandle()
notf.getFileHandle()
cause reasons. -
The Nim compiler does accept arguments in the form
-a=value
or--arg=value
even tho if you look at the usage it only has arguments passed as-a:value
or--arg:value
. (Important for Makefiles) -
When defining a byte array, you also need to indicate at least in the first value that it's a byte array, bit weird but ok (https://forum.nim-lang.org/t/4322)
Byte array in C#:
byte[] buf = new byte[5] {0xfc,0x48,0x81,0xe4,0xf0,0xff}
Byte array in Nim:
var buf: array[5, byte] = [byte 0xfc,0x48,0x81,0xe4,0xf0,0xff]
Interesting Nim libraries
- https://github.com/dom96/jester
- https://github.com/pragmagic/karax
- https://github.com/Niminem/Neel
- https://github.com/status-im/nim-libp2p
- https://github.com/PMunch/libkeepass
- https://github.com/def-/nim-syscall
- https://github.com/tulayang/asyncdocker
- https://github.com/treeform/ws
- https://github.com/guzba/zippy
- https://github.com/rockcavera/nim-iputils
- https://github.com/FedericoCeratto/nim-socks5
- https://github.com/CORDEA/backoff
- https://github.com/treeform/steganography
- https://github.com/miere43/nim-registry
- https://github.com/status-im/nim-daemon
Nim for implant dev links
- https://web.archive.org/web/20210117002945/https://secbytes.net/implant-roulette-part-1:-nimplant/
- https://securelist.com/zebrocys-multilanguage-malware-salad/90680/
- https://github.com/MythicAgents/Nimplant
- https://github.com/elddy/Nim-SMBExec
- https://github.com/elddy/NimScan