Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/a229acff4e0605ad24eaf3d9c44fdb1b.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.DarkKomet.irv
Vulnerability: Insecure Permissions
Description: DarkKomet.irv creates an insecure dir named "Windupdt" under c:\ drive, granting change (C) permissions to authenticated user group. Standard users can rename the malware and reboot to disable it or replace it with their own executable to escalate privileges when a privileged user logs on. DarkKomet also creates auto start registry keys under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run and HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon "Userinit" and drops three other files under "AppData\Local\Temp". To successfully rename the malware we have to call Windows "attrib -h" command to unhide the executable or the rename will fail.

Type: PE32
MD5: a229acff4e0605ad24eaf3d9c44fdb1b
Vuln ID: MVID-2021-0105
Dropped files: winupdate.exe, [TGS]CAPUB V1.11.EXE, [TGS]CAPUB V1.11.DLL, dclogs.sys
Disclosure: 02/21/2021


Exploit/PoC:
#include "stdio.h"
#include "windows.h"

void main(void){
   
    system("attrib -h C:\\Windupdt\\winupdate.exe");
    puts("Unhiding the malware to rename it...");
    system("RENAME C:\\Windupdt\\winupdate.exe  13");
    
    Sleep(1000);
    printf("[+] Disabled persistence by renaming winupdate.exe to 13 ...\n");
    printf("Restart your computer ...");

    puts("[+] Backdoor.Win32.DarkKomet.irv PWNED!\n");
    puts("[+] MD5: a229acff4e0605ad24eaf3d9c44fdb1b\n");
    puts("[+] By Malvuln\n");
    system("pause");
  
}

C:\Windupdt BUILTIN\Administrators:(OI)(CI)(ID)F
            NT AUTHORITY\SYSTEM:(OI)(CI)(ID)F
            BUILTIN\Users:(OI)(CI)(ID)R
            NT AUTHORITY\Authenticated Users:(ID)C
            NT AUTHORITY\Authenticated Users:(OI)(CI)(IO)(ID)C


C:\>dir \Windupdt
 Volume in drive C has no label.

 Directory of C:\Windupdt

C:\>dir /a \Windupdt
 Volume in drive C has no label.

 Directory of C:\Windupdt

06/14/2012  10:58 PM         1,433,088 winupdate.exe
               1 File(s)      1,537,340 bytes
               2 Dir(s)  49,992,314,880 bytes free


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