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Message-ID: <CAAHK0WTKwocbn-zPRGMwdpCY5HL49S4MDgvL655L0eNnac6U=Q@mail.gmail.com>
Date: Thu, 5 May 2022 14:20:47 -0400
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] REvil.Ransom / Code Execution

Discovery / credits: Malvuln - (John Page - aka hyp3rlinx) (c) 2022
Original source:
https://malvuln.com/advisory/4c5c1731481ea8d67ef6076810c49e00.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: REvil.Ransom
Vulnerability: Code Execution
Description: REvil looks for and executes DLLs in its current directory.
Therefore, we can hijack a vuln DLL, execute our own code, control and
terminate the malware pre-encryption. The exploit dll checks if the current
directory is "C:\Windows\System32", if not we grab our process ID and
terminate. We do not need to rely on hash signatures or third-party
products, the malwares flaw does the work for us. Endpoint protection
systems and or antivirus can potentially be killed prior to executing
malware, but this method cannot as there's nothing to kill the DLL just
lives on disk waiting. From a defensive perspective you can add the DLLs to
a specific network share containing important data as a layered approach.
All basic tests were conducted successfully in a virtual machine
environment.
Family: REvil
Type: PE32
MD5: 4c5c1731481ea8d67ef6076810c49e00
Vuln ID: MVID-2022-0583
Disclosure: 05/05/2022
Video PoC URL: https://www.youtube.com/watch?v=6LYBPP4N5yA

Exploit/PoC:
1) Compile the following C code as "urlmon.dll" 32bit
2) Place the DLL in same directory as the ransomware
3) Optional - Hide it: attrib +s +h "urlmon.dll"
4) Run the malware

#include "windows.h"

//By malvuln - 5/5/2022
//Purpose:
//gcc -c urlmon.c -m32
//gcc -shared -o urlmon.dll urlmon.o -m32

BOOL APIENTRY DllMain(HINSTANCE hInst, DWORD reason, LPVOID reserved){
  switch (reason) {
  case DLL_PROCESS_ATTACH:
   MessageBox(NULL, "Code Exec", "by malvuln", MB_OK);
   TCHAR buf[MAX_PATH];
   if(GetCurrentDirectory(MAX_PATH, buf))
   if(strcmp("c:\\Windows\\system32", buf) != 0){
    HANDLE handle = OpenProcess(PROCESS_TERMINATE, FALSE, getpid());
     if (NULL != handle) {
        TerminateProcess(handle, 0);
       CloseHandle(handle);
     }
   }
    break;
  }
  return TRUE;
}

Disclaimer: The information contained within this advisory is supplied
"as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory,
provided that it is not altered except by reformatting it, and that due
credit is given. Permission is explicitly given for insertion in
vulnerability databases and similar, provided that due credit is given to
the author. The author is not responsible for any misuse of the information
contained herein and accepts no responsibility for any damage caused by the
use or misuse of this information. The author prohibits any malicious use
of security related information or exploits by the author or elsewhere. Do
not attempt to download Malware samples. The author of this website takes
no responsibility for any kind of damages occurring from improper Malware
handling or the downloading of ANY Malware mentioned on this website or
elsewhere. All content Copyright (c) Malvuln.com (TM).
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