REvil looks for and executes DLLs in its current directory. Therefore, we can potentially hijack a vulnerable DLL to execute our own code, control and terminate the malware pre-encryption. The exploit DLL will check if the current directory is "C:\Windows\System32" and if not we grab our process ID and terminate. We do not need to rely on a hash signature or third-party product, the malware's own vulnerability 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 there's nothing to kill the DLL that 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.
268cdb6f1c42815be3079d4e45fd4bf006bd0c4df1203a033c3ddc55bcdb5be7Discovery / credits: Malvuln - malvuln.com (c) 2022
Original source: https://malvuln.com/advisory/7d7ee58c2696794b3be958b165eb61a9.txt
Contact: [email protected]
Media: twitter.com/malvuln
Threat: REvil Ransom
Vulnerability: Code Execution
Description: REvil 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 malwares own vulnerability 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: REvil
Type: PE32
MD5: 7d7ee58c2696794b3be958b165eb61a9
Vuln ID: MVID-2022-0577
Disclosure: 05/03/2022
Video PoC URL: https://www.youtube.com/watch?v=WnDxcYzfbUQ
Exploit/PoC:
1) Compile the following C code as "CLDAPI.dll"
2) Place the DLL in same directory as the ransomware
3) Optional - Hide it: attrib +s +h "CLDAPI.dll"
4) Run Conti
#include "windows.h"
#include "stdio.h"
//By malvuln
//Purpose: Code Execution
//Target: REvi Ransomware
//MD5: 7d7ee58c2696794b3be958b165eb61a9
/** 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 CLDAPI.c -m32
//gcc -shared -o CLDAPI.dll CLDAPI.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));
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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