CVE-2026-3242 Concrete CMS below 9.4.8 is vulnerable to Stored XSS in the Switch Language block

What is CVE-2026-3242?

CVE-2026-3242 is a medium-severity cross-site scripting vulnerability in Concretecms Concrete Cms, published on 4 Mar 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

Official description

In Concrete CMS below version 9.4.8, a rogue administrator can add stored XSS via the Switch Language block.  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 M3dium for reporting.

Weakness: CWE-79

Which versions are affected by CVE-2026-3242?

2 open source packages ship an affected version, including concrete5/concrete5. It affects 1 product.

Products include Concretecms Concrete Cms.

How do I fix CVE-2026-3242?

Upgrade concrete5/concrete5 to 9.4.8 or later.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2026-3242 being exploited?

There is no known exploitation of CVE-2026-3242 in the wild and no public exploit code.

Other vulnerabilities in Concretecms Concrete Cms

• CVE-2023-48648 Concrete CMS allows unauthorized access because directories can be created with insecure permissions Critical 9.8
• CVE-2022-21829 Code injection in concrete CMS Critical 9.8
• CVE-2021-22958 Server-Side Request Forgery vulnerability in concrete5 Critical 9.8
• CVE-2021-40098 Path traversal in n/a Critical 9.8
• CVE-2026-8134 Concrete CMS Vulnerable to Relative Path Traversal Critical 9.4

All Concretecms Concrete Cms vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-w9qg-chfh-g3q9.