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MEDIUM severity

Concrete CMS has a stored Cross-site Scripting (XSS) vulnerabilityGHSA-w9qg-chfh-g3q9

MEDIUMFix: concretecms/concretecms#12826

GHSA-w9qg-chfh-g3q9 is a medium-severity (CVSS 4.8) Cross-site Scripting (XSS) vulnerability in concrete5/concrete5. A fix is available for concrete5/concrete5 — see the affected versions and patch details below.

Also known asCVE-2026-3242
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-w9qg-chfh-g3q9.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk
0.00%0.26%0.51%0.77%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐘concrete5/concrete5

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistconcrete5/concrete5all versions9.4.8composer require concrete5/concrete5:^9.4.8

Affected Products

1 product · 1 configurations
Application
concrete cmsconcretecms
< 9.4.8
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for concrete5/concrete5, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update concrete5/concrete5 to 9.4.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w9qg-chfh-g3q9 is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

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 thanks M3dium for reporting.
O3 Security · Impact-Aware SCA

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Concrete CMS has a stored Cross-site Scripting (XSS)…