What’s Vulnerable › Vulnerabilities

CVE-2026-3240: Concrete CMS below 9.4.8 is vulnerable to Stored XSS via Legacy form

• Severity: medium (CVSS 4.8 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: yes
• Published: 2026-03-04 · updated 2026-06-17
• Weakness: CWE-79

Description

In Concrete CMS below version 9.4.8, a user with permission to edit a page with element Legacy form can perform a stored XSS attack towards high-privilege accounts via the Question field. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 4.8 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N Thanks minhnn42, namdi and quanlna2 from VCSLab-Viettel Cyber Security for reporting.

Affected products

• Concrete CMS: before 9.4.8 — fixed in 9.4.8

How to fix

Upgrade to a fixed version: Concrete CMS 9.4.8. Check the vendor advisory for mitigations.

References

• https://documentation.concretecms.org/9-x/developers/introduction/version-history/948-release-notes
• https://github.com/concretecms/concretecms/pull/12826

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