Authored by malvuln | Site malvuln.com

MaskPE by yzkzero is a tool for implanting backdoors in existing PE files. The backdoor tool does not properly check the files it loads and falls victim to a file based local buffer overflow.

Discovery / credits: Malvuln - malvuln.com (c) 20211
Original source: https://malvuln.com/advisory/170d3ccf9f036c552aef6690bf419b2e.txt
Contact: [email protected]
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Nucleroot.t - MaskPE 1.6
Vulnerability: File Based Buffer Overflow
Description: 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: 170d3ccf9f036c552aef6690bf419b2e
Vuln ID: MVID-2021-0028
Network Access: Local
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/15/2021

Memory Dump:
This dump file has an exception of interest stored in it.
The stored exception information can be accessed via .ecxr.
(88c.14b0): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=41414101 esi=00000003 edi=00000003
eip=773ced3c esp=0019e7a8 ebp=0019e938 iopl=0 nv up ei pl nz na po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00200202
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400 ret 14h
0:000> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************


FAULTING_IP:
Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+8f43
00408f43 813850450000 cmp dword ptr [eax],4550h

EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 00408f43 (Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+0x00008f43)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000000
Parameter[1]: 456c4141
Attempt to read from address 456c4141

PROCESS_NAME: Backdoor.Win32.Nucleroot.t.170d3ccf9f036c552aef6690bf419b2e.exe

OVERLAPPED_MODULE: Address regions for 'linkinfo' and 'xmllite.dll' overlap

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: 456c4141

READ_ADDRESS: 456c4141

FOLLOWUP_IP:
Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+8f43
00408f43 813850450000 cmp dword ptr [eax],4550h

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG: 0

APPLICATION_VERIFIER_FLAGS: 0

FAULTING_THREAD: 000014b0

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 004048c2 to 00408f43

STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be wrong.
0019f0c8 004048c2 00000001 0019fb74 0019f438 Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+0x8f43
0019fc38 7739fa0d 000307d0 00000018 00000000 Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+0x48c2
0019fc84 7674ac66 0019fe3c 00000001 0019fcac ntdll!RtlFreeHeap+0x7cd
0019fd30 7674a757 00000000 00000000 00000000 KERNELBASE!LocalBaseRegOpenKey+0x176
0019fe48 0042752c 76e34fb0 00000000 0031e000 KERNELBASE!RegOpenKeyExInternalW+0x137
00000000 00000000 00000000 00000000 00000000 Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+0x2752c


STACK_COMMAND: ~0s; .ecxr ; kb

SYMBOL_STACK_INDEX: 0

SYMBOL_NAME: Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+8f43

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e

IMAGE_NAME: Backdoor.Win32.Nucleroot.t.170d3ccf9f036c552aef6690bf419b2e.exe

DEBUG_FLR_IMAGE_TIMESTAMP: 4449d126

FAILURE_BUCKET_ID: STRING_DEREFERENCE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Nucleroot.t.170d3ccf9f036c552aef6690bf419b2e.exe!Unknown

BUCKET_ID: APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141_Backdoor_Win32_Nucleroot_t_170d3ccf9f036c552aef6690bf419b2e+8f43

Followup: MachineOwner



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

Load it into MaskPE and KABOOM!


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