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
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Windows_10_1507 | Microsoft | * | 10.0.10240.20978 (excluding) |
| Windows_10_1607 | Microsoft | * | 10.0.14393.7969 (excluding) |
| Windows_10_1809 | Microsoft | * | 10.0.17763.7136 (excluding) |
| Windows_10_21h2 | Microsoft | * | 10.0.19044.5737 (excluding) |
| Windows_10_22h2 | Microsoft | * | 10.0.19045.5737 (excluding) |
| Windows_11_22h2 | Microsoft | * | 10.0.22621.5189 (excluding) |
| Windows_11_23h2 | Microsoft | * | 10.0.22631.5189 (excluding) |
| Windows_11_24h2 | Microsoft | * | 10.0.26100.3775 (excluding) |
| Windows_server_2008 | Microsoft | –sp2 (including) | –sp2 (including) |
| Windows_server_2008 | Microsoft | r2-sp1 (including) | r2-sp1 (including) |
| Windows_server_2012 | Microsoft | - (including) | - (including) |
| Windows_server_2012 | Microsoft | r2 (including) | r2 (including) |
| Windows_server_2016 | Microsoft | * | 10.0.14393.7969 (excluding) |
| Windows_server_2019 | Microsoft | * | 10.0.17763.7136 (excluding) |
| Windows_server_2022 | Microsoft | * | 10.0.20348.3453 (excluding) |
| Windows_server_2022_23h2 | Microsoft | * | 10.0.25398.1551 (excluding) |
| Windows_server_2025 | Microsoft | * | 10.0.26100.3775 (excluding) |
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