UAC-SilentClean: SilentClean UAC bypass via binary planting
SilentClean UAC bypass via binary planting
This project implements a DLL planting technique to bypass UAC Always Notify and execute code in a high integrity process.
When the SilentCleanup task is launched, dismhost searches for the non-existing DLL api-ms-win-core-kernel32-legacy-l1.dll under:
C:\Users\USER\Appdata\Local\Microsoft\WindowsApps
The above path exists by default in the PATH of the user.
By crafting a malicious DLL and placing it in the above directory, it will be loaded by dismhost.exe and executed with High Integrity privileges.
Implementation
The project consists of:
- SilentClean .NET project – Launching SilentClean scheduled task with the use of the TaskScheduler library
- DLLmain_template.c – A DLL skeleton that will spawn a process and inject the shellcode of our choice. The sample provided implements a simple CreateRemoteThread injector.
- Cobalt strike aggressor script responsible for:
- Generating the shellcode byte array
- Replacing dllmain_template.c with the above shellcode
- Compile the dll with mingw
- Upload the dll to the required path
- Execute .NET binary SilentClean.exe through Execute-Assembly to launch the scheduled task
Configuration
- Feel free to replace the injection method in the RunMe function of dllmain_template.c. This is just a POC
- The current spawned process to inject to is cmd.exe.
- No shellcode encryption/compression has been baked in. As such the DLL generated will probably be flagged by an AV
- x86_64-w64-mingw32 and headers are required to be installed on the building system
- If CNA can not find mingw replace the variables $mingwgcc $mingwdllwrap with your path
- Compile SilentClean .NET project and place the executable in the same folder as the CNA script
Versions tested
- Microsoft Windows 10 – 1909 18363.1110
- Microsoft Windows 10 – 1909 18363.1082
- Microsoft Windows 10 – 1809 17763.1457
