What’s Vulnerable › Vulnerabilities
CVE-2026-81917: Concrete CMS below 9.5.3 is vulnerable to Stored XSS in the Document Library block file description and tags
- Severity: medium (CVSS 5.4 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-09-11 · updated 2026-09-18
- Weakness: CWE-79
Description
Concrete CMS below 9.5.3 does not apply HTML output escaping to the file description and tags fields when rendering the Document Library block, so a user with permission to edit file properties could store a script payload that executed in the browser of any visitor to a page displaying the block with the description or tags column enabled, including unauthenticated visitors. Successful exploitation could allow theft of session data or actions performed in the visitor's context. The block controller returned the description and tags values without the h() escaping already applied to the title column, and the block view template wrote the returned value directly into the results table The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.1 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:L/VA:N/SC:H/SI:H/SA:N. Thanks Nguyen Manh Thuan for reporting.
Affected products
- Concrete CMS: before 9.5.3 — fixed in 9.5.3
How to fix
Upgrade to a fixed version: Concrete CMS 9.5.3. Check the vendor advisory for mitigations.
References
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