Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/de613b96174056ef22b42e112d0e61a5.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Trojan-Spy.Win32.KeyLogger.qt
Vulnerability: Insecure Permissions
Description: KeyLogger.qt creates a hidden insecure dir named "config" under c:\ drive and grants change (C) permissions to the authenticated user group. Standard users can rename "rundll32.exe" dropped by the keylogger to disable it or replace with their own executable. Then wait for a privileged user to logon to the infected machine to potentially escalate privileges.
Type: PE32
MD5: de613b96174056ef22b42e112d0e61a5
Vuln ID: MVID-2021-0124
Dropped files: rundll32.exe
Disclosure: 03/10/2021

Exploit/PoC:
#include "windows.h"

void main(void){

system("attrib -s -h C:\\config\\rundll32.exe");
system("rename C:\\config\\rundll32.exe 13");

Sleep(1000);
puts("[+] Disabled by renaming C:\\config\\rundll32.exe to 13 ...\n");
Sleep(1000);

puts("[+] Trojan-Spy.Win32.KeyLogger.qt PWNED!");
puts("[+] MD5: de613b96174056ef22b42e112d0e61a5");
puts("[+] By Malvuln");
system("pause");
}

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

 Directory of C:\config

File Not Found

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

 Directory of C:\config

06/16/2012  12:54 AM           585,778 rundll32.exe
               1 File(s)        585,778 bytes


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