CVE-2026-3240: Concrete5/concrete5 Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-45fj-fvmm-xcc5
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CWE-79
Published
Advisory Summary

CVE-2026-3240 is a MODERATE cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Concrete5/concrete5 libraries in the Packagist ecosystem. The issue involves concrete cms has a stored cross-site scripting (xss) vulnerability. Remediation is available by upgrading affected packages to version 9.4.8.

CVE-2026-3240 at a Glance

CVE Identifier CVE-2026-3240
GHSA Identifier GHSA-45fj-fvmm-xcc5
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Concrete5/concrete5
Package Ecosystem Packagist
Published Date
Last Updated

How to Fix CVE-2026-3240

To remediate this vulnerability, upgrade all affected Concrete5/concrete5 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

concrete5/concrete5 fixed: 9.4.8 
Upgrade concrete5/concrete5 to 9.4.8
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for concrete5/concrete5

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-3240, inspect your project dependencies for Concrete5/concrete5:

inspect dependencies for concrete5/concrete5

Analyze the terminal output to locate any version of Concrete5/concrete5 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 9.4.8), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Concrete5/concrete5, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-3240 Affected Concrete5/concrete5 Versions

1 component(s)
Fixed Versions:
9.4.8
Product / Package Ecosystem Affected Versions Fixed Version
concrete5/concrete5
 Packagist
< 9.4.8
9.4.8

References

NVD — CVE-2026-3240 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-3240
Concrete5/concrete5 Source Repository REPOSITORY
https://github.com/concretecms/concretecms/pull/12826
documentation.concretecms.org/9-x/developers/intr... WEB
https://documentation.concretecms.org/9-x/developers/introduction/version-history/948-release-notes
Concrete5/concrete5 Source Repository REPOSITORY
https://github.com/concretecms/concretecms

Frequently Asked Questions

What is CVE-2026-3240?
CVE-2026-3240 is a security vulnerability in Concrete5/concrete5 involving Concrete CMS has a stored Cross-site Scripting (XSS) vulnerability under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Concrete5/concrete5 versions are affected?
Affected versions include releases prior to 9.4.8 across affected packages: concrete5/concrete5.
What version fixes CVE-2026-3240?
Upgrading to 9.4.8 (or the latest patched release for your respective branch) resolves the vulnerability.
Is concrete5/concrete5 affected?
Yes, concrete5/concrete5 is affected in releases prior to 9.4.8. Upgrade your dependency to 9.4.8 or later.
What CWE is associated with CVE-2026-3240?
CVE-2026-3240 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Packagist dependencies for CVE-2026-3240?
Run the dependency tree command: 'inspect dependencies for concrete5/concrete5'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-45fj-fvmm-xcc5",
  "modified" : "2026-03-04T21:36:26Z",
  "published" : "2026-03-04T03:31:34Z",
  "aliases" : [ "CVE-2026-3240" ],
  "summary" : "Concrete CMS has a stored Cross-site Scripting (XSS) vulnerability",
  "details" : "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. \n\nThe Concrete CMS security team thanks minhnn42, namdi and quanlna2 from VCSLab-Viettel Cyber Security for reporting.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "concrete5/concrete5"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "9.4.8"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-3240"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/concretecms/concretecms/pull/12826"
  }, {
    "type" : "WEB",
    "url" : "https://documentation.concretecms.org/9-x/developers/introduction/version-history/948-release-notes"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/concretecms/concretecms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-04T21:36:26Z",
    "nvd_published_at" : "2026-03-04T03:16:04Z"
  }
}