Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/9d296ebd6b4f79457fcc61e38dcce61e.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Trojan.Win32.Pincav.cmfl
Vulnerability: Insecure Permissions 
Description: The trojan creates an insecure dir named "Windupdt" under c:\ drive, granting change (C) permissions to authenticated users 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. The malware also creates registry key under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run for persistence. 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: 9d296ebd6b4f79457fcc61e38dcce61e
Vuln ID: MVID-2021-0104
Dropped files: winupdate.exe
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);
    puts("[+] Disabled persistence by renaming winupdate.exe to 13 ...\n");
    puts("Restart your computer ...");

    puts("[+] Trojan.Win32.Pincav.cmfl PWNED!\n");
    puts("[+] MD5: 9d296ebd6b4f79457fcc61e38dcce61e\n");
    puts("[+] By Malvuln\n");
    system("pause");
  
}

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

 Directory of C:\Windupdt

06/14/2012  11:46 PM           707,094 winupdate.exe
               1 File(s)        707,094 bytes
               2 Dir(s)  49,773,490,176 bytes free



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