Discovery / credits: Malvuln - malvuln.com (c) 2022
Original source: https://malvuln.com/advisory/40f2238875fcbd2a92cfefc4846a15a8.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Ransom.AvosLocker
Vulnerability: Code Execution
Description: The ransomware looks for and executes DLLs in its current directory. Therefore, we can potentially hijack a vuln DLL execute our own code, control and terminate the malware pre-encryption. The exploit dll will check 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 signature or third-party product, the malware will do the work for us. Endpoint protection systems and or antivirus can potentially be killed prior to executing malware, but this method cannot as theres nothing to kill the DLL just lives on disk waiting. From 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: AvosLocker
Type: PE32
MD5: 40f2238875fcbd2a92cfefc4846a15a8
Vuln ID: MVID-2022-0573
Disclosure: 05/02/2022
Video PoC URL: https://www.youtube.com/watch?v=jCxG46dEmso

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

#include "windows.h"
#include "stdio.h"

//By malvuln - 5/2/2022
//Vuln: Code Execution
//Target: Ransom.AvosLocker
//MD5: 40f2238875fcbd2a92cfefc4846a15a8
/** DISCLAIMER:
Author is NOT responsible for any damages whatsoever by using this software or improper malware
handling. By using this code you assume and accept all risk implied or otherwise.
**/

//gcc -c mpr.c -m32
//gcc -shared -o mpr.dll mpr.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];
   GetCurrentDirectory(MAX_PATH, TEXT(buf));
   //printf("Current directory: %s\n", buf);
   //check the path
   int rc = strcmp("C:\\Windows\\System32", TEXT(buf));
     if(rc != 0){
     HANDLE handle = OpenProcess(PROCESS_TERMINATE, FALSE, getpid());
     if (NULL != handle) {   
        TerminateProcess(handle, 0);
       CloseHandle(handle);
     }
   }
    break;
  }
  return TRUE;
}


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