Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/c60f00700bd73ca369195bd32a3f16a3.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: HEUR.Trojan.Win32.Generic
Vulnerability: Insecure Permissions
Description: The specimen creates a dir named "RECYCLER" under c:\ drive and grants change (C) permissions to the authenticated user group. Within the RECYCLER dir exists an hidden dir named with security identifier (SID), which in turn contains a dropped executable named "i7764tg.exe". Standard users can rename the executable dropped by the malware to disable it or replace it with their own executable. Then wait for a privileged user to logon to the infected machine to potentially escalate privileges.
Type: PE32
MD5: c60f00700bd73ca369195bd32a3f16a3
Vuln ID: MVID-2021-0136
Dropped files: i7764tg.exe
Disclosure: 03/19/2021


Exploit/PoC:
C:\>cacls \RECYCLER
C:\RECYCLER 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:\RECYCLER>dir /a
 Volume in drive C has no label.

 Directory of C:\RECYCLER

03/02/2021  11:06 AM    <DIR>         S-1-5-21-0243556031-888888379-781863308-9761
               0 File(s)              0 bytes

C:\RECYCLER>cd S-1-5-21-0243556031-888888379-781863308-9761

C:\RECYCLER\S-1-5-21-0243556031-888888379-781863308-9761>dir /a
 Volume in drive C has no label.

 Directory of C:\RECYCLER\S-1-5-21-0243556031-888888379-781863308-9761

03/02/2021  11:06 AM                63 Desktop.ini
06/17/2012  02:29 AM            45,056 i7764tg.exe


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).