HEUR.Trojan.Win32.Generic / Insecure Permissions

[malvuln <malvuln13 () gmail com>]

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


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