Summary
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 thanks minhnn42, namdi and quanlna2 from VCSLab-Viettel Cyber Security for reporting.
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-3240? CVE-2026-3240 is a medium-severity cross-site scripting (XSS) vulnerability in concrete5/concrete5 (composer), affecting versions < 9.4.8. It is fixed in 9.4.8. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- Which versions of concrete5/concrete5 are affected by CVE-2026-3240? concrete5/concrete5 (composer) versions < 9.4.8 is affected.
- Is there a fix for CVE-2026-3240? Yes. CVE-2026-3240 is fixed in 9.4.8. Upgrade to this version or later.
- Is CVE-2026-3240 exploitable, and should I be worried? Whether CVE-2026-3240 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-3240 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-3240? Upgrade
concrete5/concrete5to 9.4.8 or later.