SHARE
RedPeanut : Small RAT Developed in .Net Core 2 & Its Agent in .Net 3.5 / 4.0

RedPeanut is a small RAT developed in .Net Core 2 and its agent in .Net 3.5 / 4.0. RedPeanut code execution is based on shellcode generated with DonutCS. It is therefore a hybrid, although developed in .Net it does not rely solely on the Assembly.Load.

This increases the detection surface, but allows us to practice and experiment with various evasion techniques related to the dotnet environment, process management and injection.

This behavior can be changed at rutime with the “managed” and “unmanaged” commands. If you are interested in a .Net C2 Framework that is consistent and can be used in an enagement, I suggest Covenant.

RedPeanut is weaponized with:

  • GhostPack
  • SharpGPOAbuse
  • SharpCOM
  • EvilClippy
  • DotNetToJS
  • SharpWeb
  • Modified version of PsExec
  • SharpSploit
  • TikiTorch

Also Read – DDoor : Cross Platform Backdoor Using DNS txt Records

RedPeanut Agent

The RedPeanut agent can be compiled in .Net 3.5 and 4.0 and has pivoting capabilities via NamedPipe. The agent, when executed in an unmanaged mode, performs its own critical tasks in a separate process to prevent the AV response to detection or error during execution make you lose the whole agent.

The execution flow is as follow:

  1. Process creation
  2. Inject static shellcode generated with DonutCS
  3. The loader loads and executes the stager or module

The agent currently only supports https channel.

C2 Channel

The agent checkin protocol is very simple:

  1. The stager requires an agent id, the message is encrypted with RC4 with the shared serverkey
  2. The server decrypt the message, compile and sends the agent, generate and send KEY and IV for future communications AES encryption, the message is encrypted RC4
  3. The stager decrypt the message and load the agent via Assembly.Load
  4. The agent sends a checkin message to the server, the message is encrypted with AES

Alternatively, the covered channel feature can be activated(at the moment it is just a PoC). The idea is to imitate the web traffic carried out by a real user. Usually a web page is composed of the html page and all the objects necessary for its display as css, images, etc. At the request of a new task the answer from the server will not be directly the encrypted task but an html page from which to extract the link to the image that will have embedded the encrypted task. The http request for the image will contain the Referer header.

Content Delivery

Content delivery is organized in 4 channels:

  1. C2 Channe customizable via profile
  2. Dynamic content generated/managed by RedPeanut customizable via profile
  3. Static content mapped to /file/
  4. Covered channel for the recovery of the image containing the payload mapped to /images/

Profiles

RedPeanut capability of customization of network footprint both server side and client side. The properties that can be set are:

  • General
    • Delay (between requests)
    • ContentUri (url of dynamic content eg. dll hta etc.)
    • UserAgent
    • Spawn (the process to create to perform critical tasks)
    • HtmlCovered (Enable covered channel)
    • TargetClass (Class to search for image recover)
  • Http Get
    • ApiPath (comma separated list of url es /news-list.jsp,/antani.php etc.)
    • Server
      • Prepend
      • Append
      • Headers (name and value pair for http headers)
    • Client
      • Headers    
  • Http Post
    • ApiPath (comma separated list of url es /news-list.jsp,/antani.php etc.)
    • Param (the name of the post request payload parameter)
    • Mask (format for interpreting the key value pair eg {0}={1}) (need more work…)
    • Server
      • Prepend
      • Append
      • Headers (name and value pair for http headers)
    • Client
      • Headers

Domain Fronting

To enable the domain fronting support it is necessary to value the “Host” header in the client section, both post and get (exemplified in the default profile 2)

PowerShellExecuter

The PowerShellExecuter module allows you to execute oneliner commands or files in a runspace with AMSI bypass, Logging bypass and PowerView already loaded.

Launchers

  • Exe
  • Dll
  • PowerShell
  • Hta (vbs,powershell)
  • InstallUtil
  • MSBuild
  • MacroVba

Local modules

  • EvilClippy

Agent Tasks

  • Upload
  • DownLoad
  • SharpWeb
  • SharpWmi
  • SharpUp
  • UACBypass Token Duplication
  • SharpDPAPIVaults
  • SharpDPAPITriage
  • SharpDPAPIRdg
  • SharpDPAPIMasterKeys
  • SharpDPAPIMachineVaults
  • SharpDPAPIMachineTriage
  • SharpDPAPIMachineMasterKeys
  • SharpDPAPIMachineCredentials
  • SharpDPAPICredentials
  • SharpDPAPIBackupKey
  • Seatbelt
  • SafetyKatz
  • RubeusTriage
  • RubeusTgtDeleg
  • RubeusS4U
  • RubeusRenew
  • RubeusPurge
  • RubeusPtt
  • RubeusMonitor
  • RubeusKlist
  • RubeusKerberoast
  • RubeusHash
  • RubeusHarvest
  • RubeusDump
  • RubeusDescribe
  • RubeusCreateNetOnly
  • RubeusChangePw
  • RubeusASREPRoast
  • RubeusAskTgt
  • SharpCOM
  • SharpGPOAddUserRights
  • SharpGPOAddStartupScript
  • SharpGPOAddLocalAdmin
  • SharpGPOAddImmediateTask
  • PowerShellExecuter
  • LatteralMSBuild
  • SharpPsExec
  • SharpAdidnsdump
  • PPIDAgent
  • SpawnAsAgent
  • SpawnShellcode
  • SpawnAsShellcode
  • SharpMiniDump

Persistence

  • Autorun
  • Startup
  • WMI
  • CRL

BlockDlls

Starting with version 0.3.0 RedPeanutAgent supports the blockdlls command. With this option enabled, child processes that are created to perform tasks in unmanaged mode are created with the attribute PROCESS_CREATION_MITIGATION_POLICY_BLOCK_NON_MICROSOFT_BINARIES_ALWAYS_ON. This attribute prevents the process of loading dlls that are not signed by Microsoft, this could protect our tasks from AV and EDR hooking techniques.

Direct Sysstem Call and Dynamic Dll Loading

RedPeanutAgent uses Dynamic Dll loading to avoiding using of suspicious Dll Imports. Credits for Dynamic Dll Loading goes to @TheRealWover, @cobbr_io and @FuzzySec for their work in SharpSploit.

Some AV and EDR vendors used hooking technique to keep track of activities. To avoid using hooked syscall RedPeanutAgent uses direct syscall, auto injecting the necessary code. Credits for Direct Syscall goes to @Cneelis

Running

To run RedPeanut you need to have dotnet installed. To install dotnet on Kali:

wget -qO- https://packages.microsoft.com/keys/microsoft.asc | gpg –dearmor > microsoft.asc.gpg
mv microsoft.asc.gpg /etc/apt/trusted.gpg.d/
wget -q https://packages.microsoft.com/config/debian/9/prod.list
mv prod.list /etc/apt/sources.list.d/microsoft-prod.list
chown root:root /etc/apt/trusted.gpg.d/microsoft.asc.gpg
chown root:root /etc/apt/sources.list.d/microsoft-prod.list

apt-get install apt-transport-https
apt-get update
apt-get install dotnet-sdk-2.1

git clone –recursive https://github.com/b4rtik/RedPeanut.git

For the covered channel functionality it is necessary to install the libgdiplus library, therefore:

For linux users:

apt-get install -y libgdiplus

For OSx

brew install mono-libgdiplus

Assembly signing key generation

C:\Program Files (x86)\Microsoft Visual Studio\2017\Community>sn.exe -k 4096 key.snk

Than copy key.snk in Workspace/KeyFile

root@kali:~# cd RedPanut
root@kali:~/RedPeanut# dotnet run
Using launch settings from /root/Projects/RedPeanut/Properties/launchSettings.json…
Enter password to encrypt serverkey:

[*] No profile avalilable, creating new one…
[RP] >

Shellcode Generator

DonutCS is a shellcode generation tool that creates position-independant shellcode payloads from .NET Assemblies. This shellcode may be used to inject the Assembly into arbitrary Windows processes. Given an arbitrary .NET Assembly, parameters, and an entry point (such as Program.Main), it produces position-independent shellcode that loads it from memory. The .NET Assembly can either be staged from a URL or stageless by being embedded directly in the shellcode.

CLR Persistence

The CLR persistence technique was presented for the first time in this post by @Am0nsec. The technique consists in carrying out the application domain manager hooking. As described in the post, the assembly to carry out hooking is necessary which is available in the GAC. An assembly to be used from the GAC must be strong-named and then signed with a key. The CLR persistence module needs a key to be able to sign the assemblies, which can be generated with the sn.exe tool as follows:

**********************************************************************
** Visual Studio 2017 Developer Command Prompt v15.9.3
** Copyright (c) 2017 Microsoft Corporation
**********************************************************************

C:\Program Files (x86)\Microsoft Visual Studio\2017\Community>sn.exe -k 4096 key.snk

Copy the key.snk file to Workspace/KeyFile folder. This file will be used to sign the assembly for persistence.

Tools Updating

Some of the well-known tools present in RedPeanut such as the GhostPack tools are wrapped in full and executed on the client side. To update the tools, for example SeatBelt, without updating the entire repository is necessary: Clone the Seatbelt repository, rename the “Main” method in “Execute”, insert the public modifier and recompile as dll. The dll must be compressed and encoded in Base64 with the ps RastaMouse’s script Get-CompressedShellcode.ps1