Cobaltstrike UDRL

Features:

• Redirect all WININET calls over callstack crafting
• Encrypt beacon during sleep
• Encrypt beacon heap during sleep
• Self delete of loader

Callstack exemples:

CreateThread:

InternetOpenA:

WaitForSingleObject:

1 - Create heap for beacon usage

2 - Allocation of RWX area with beacon size + UDRL size

3 - Copy the UDRL at the end of beacon in allocated area

| 0x00 | beacon | 0xBEACON_SIZE | UDRL | 0xEND_Alloc

4 - Copy the ODIN structure (heap handle, beacon addr, alloc size) to the start of allocated area (no pe header is present)

5 - Copy beacon section

6 - Resolve beacon import and patch IAT (also set hook)

7 - Patch relocation table

8 - Init the beacon

9 - Create thread on TpReleaseCleanupGroupMembers+0x450 to spoof the thread start addr & beacon run

10 - Self delete the loader

• All WININET function is hooked and use callstack crafting for all wininet call

• Sleep is hooked:

  1 - XOR the heap (random key for each sleep)

  2 - Encrypt the beacon + udrl (remember this was copied at the end of beacon) with KrakenMask (ropchain, rwx->rw, encrypt, sleep, rw->rwx)

  3 - XOR the heap

• ExitThread is hooked:

  1 - Destroy the beacon heap

  2 - Free the memory region with the beacon

  3 - Exit thread

Compile the loader and load the cna script (odin.cna)

About the cna, you need to edit path of variable $loader_path at line 11 & 38

http-beacon {
    set library "wininet";
	
}

stage {
	set smartinject "false";
	set sleep_mask "false";
}

It's a POC, be careful when using this UDRL

If you happen to have a crash, you can dm on twitter or open github issues, please send:

- Cobaltstrike profil

- Debugger screen with callstack

You need to have python on your windows machine, you have post-ex build to run python script.

Python script uses two libraries: sys and pefile

Moneta:

Pe-Sieve:

HuntSleepingBeacons:

For code:

• Callstack craffting : https://github.com/susMdT/LoudSunRun
• Some parts of code : https://www.cobaltstrike.com/product/features/user-defined-reflective-loader

For idea:

• AceLdr : https://github.com/kyleavery/AceLdr
• BokuLdr : https://github.com/boku7/BokuLoader
• KaynStrike : https://github.com/Cracked5pider/KaynStrike

Thanks to:

• chatGPT, Bakki, Caracal & CobaltAD : For debug and somes help