CVE-2025-24076 - How Improper Access Control in Windows Cross Device Service Lets Local Attackers Elevate Privileges

In June 2025, Microsoft disclosed a new vulnerability in its Windows Cross Device Service: CVE-2025-24076. This flaw can let an attacker with limited local access boost their privileges and potentially gain control over affected systems. In this post, I’ll break down how this works, what code is involved, and how someone might exploit it—with links straight to original resources.

What is the Windows Cross Device Service?

The Windows Cross Device Service helps connect a user’s devices and transfer data between them, like notifications, Clipboard history, or app activities. It typically runs as a privileged Windows service (cdpusersvc), and is always running in the background if you use features like "Continue on PC" or "Phone Link."

What’s the Problem With Access Control?

Normally, sensitive Windows services enforce strict boundaries, so regular users can’t do much damage. But with CVE-2025-24076, Microsoft admits there’s improper access control—meaning some operations that should be protected are left open to users who shouldn’t have them.

Microsoft’s advisory:
> _An attacker who successfully exploited this vulnerability could gain SYSTEM privileges._
> Reference: Microsoft Security Guide - CVE-2025-24076

Attacker is local—they have a user account on the system.

2. They discover that Cross Device Service exposes a privileged named pipe (e.g., \\.\pipe\cdpusersvc_pipe).

Improper permissions mean any user can connect to that pipe and send commands.

4. By sending certain malicious commands, the attacker can trigger the service to perform privileged actions on their behalf.

Code Snippet: Proof of Concept

Below is a simplified pseudo-Python code showing how someone could exploit such a service using a named pipe:

import win32pipe, win32file

# Connect to the vulnerable named pipe
pipe = win32file.CreateFile(
    r'\\.\pipe\cdpusersvc_pipe',
    win32file.GENERIC_READ | win32file.GENERIC_WRITE,
    , None,
    win32file.OPEN_EXISTING,
    , None)

# Craft a malicious payload (details depend on the service implementation)
payload = b"GET_SYSTEM_TOKEN"

# Send the payload
win32file.WriteFile(pipe, payload)

# Read response (could be a SYSTEM token or another elevated resource)
result = win32file.ReadFile(pipe, 4096)
print("Received:", result)

pipe.close()

Note: This code is for educational purposes and demonstrates the principle. Real exploits would look for undocumented commands or design flaws in the service.

Run any command as SYSTEM, install malware, access data, etc.

- No interaction from the victim needed—if someone already has local access (a standard user account), your machine could be compromised in seconds.

How to Protect Yourself

- Install Microsoft’s Patch: Updates are available as part of June 2025 Patch Tuesday, or check the MSRC Update Guide.

Restrict Local Access: Only let trusted users on your computer.

- Monitor for Suspicious Activity: Unusual use of cdpusersvc or new named pipe connections may be a sign someone tried this exploit.

More Resources

- Official Microsoft Advisory – CVE-2025-24076
- CERT/CC Vulnerability Note
- Deep Dive into Windows Named Pipe Security (Blog)


Summary:
CVE-2025-24076 is a classic example of how improper access control in a privileged Windows service can flip a local user into an all-powerful SYSTEM. If you haven’t patched, update ASAP. For insight into how these bugs work under the hood, keep learning—and always be careful what code you run or expose on your machine.

Timeline

Published on: 03/11/2025 17:16:30 UTC
Last modified on: 03/19/2025 02:05:34 UTC