CVE-2026-81918: Concrete CMS below 9.5.3 is vulnerable to Stored XSS via the Date Format field in the Page Attribute Display block

Severity: medium (CVSS 4.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% 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 is vulnerable to Stored XSS via the Date Format field in the Page Attribute Display block. A user with edit_page_contents permissions could store a payload which executes in the browser of any visitor who viewed a page where the block was configured to display a date-type attribute. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 4.8 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Oriol Ortiz 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

https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes

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