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



Disclaimer: The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. Permission is hereby granted for the redistribution of this advisory, provided that it is not altered except by reformatting it, and that due credit is given. Permission is explicitly given for insertion in vulnerability databases and similar, provided that due credit is given to the author. The author is not responsible for any misuse of the information contained herein and accepts no responsibility for any damage caused by the use or misuse of this information. The author prohibits any malicious use of security related information or exploits by the author or elsewhere. Do not attempt to download Malware samples. The author of this website takes no responsibility for any kind of damages occurring from improper Malware handling or the downloading of ANY Malware mentioned on this website or elsewhere. All content Copyright (c) Malvuln.com (TM).