CVE-2025-21204

Improper link resolution before file access (link following) in Windows Update Stack allows an authorized attacker to elevate privileges locally.

Weakness

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Affected Software

Potential Mitigations

• Follow the principle of least privilege when assigning access rights to entities in a software system.
• Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/132.html
• https://cwe.mitre.org/data/definitions/17.html
• https://cwe.mitre.org/data/definitions/35.html
• https://cwe.mitre.org/data/definitions/76.html

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21204
• https://www.vicarius.io/vsociety/posts/cve-2025-21204-privilege-elevation-vulnerability-in-microsoft-windows-update-stack-detection-script
• https://www.vicarius.io/vsociety/posts/cve-2025-21204-privilege-elevation-vulnerability-in-microsoft-windows-update-stack-mitigation-script