CVE-2026-8139: Concrete5/concrete5 Cross-Site Scripting Vulnerability

LOW
Advisory Identifier: GHSA-pcrh-gj77-j4mw
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CWE-79
Published
Advisory Summary

CVE-2026-8139 is a LOW 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 is vulnerable to stored xss via external-link page cvname. Remediation is available by upgrading affected packages to version 9.5.1.

CVE-2026-8139 at a Glance

CVE Identifier CVE-2026-8139
GHSA Identifier GHSA-pcrh-gj77-j4mw
Severity LOW
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-2026-8139

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: 9.5.1 
Upgrade concrete5/concrete5 to 9.5.1
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-2026-8139, 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 9.5.1), 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

Concrete CMS 9.5.0 and below is vulnerable to Stored XSS via external-link page cvName because updateCollectionAliasExternal bypasses being sanitized.

CVE-2026-8139 Affected Concrete5/concrete5 Versions

1 component(s)
Fixed Versions:
9.5.1
Product / Package Ecosystem Affected Versions Fixed Version
concrete5/concrete5
 Packagist
< 9.5.1
9.5.1

References

NVD — CVE-2026-8139 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-8139
documentation.concretecms.org/9-x/developers/intr... WEB
https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes
Concrete5/concrete5 Source Repository REPOSITORY
https://github.com/concretecms/concretecms

Frequently Asked Questions

What is CVE-2026-8139?
CVE-2026-8139 is a security vulnerability in Concrete5/concrete5 involving Concrete CMS is vulnerable to Stored XSS via external-link page cvName 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 9.5.1 across affected packages: concrete5/concrete5.
What version fixes CVE-2026-8139?
Upgrading to 9.5.1 (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 9.5.1. Upgrade your dependency to 9.5.1 or later.
What CWE is associated with CVE-2026-8139?
CVE-2026-8139 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-2026-8139?
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-pcrh-gj77-j4mw",
  "modified" : "2026-06-24T21:06:04Z",
  "published" : "2026-05-22T00:31:16Z",
  "aliases" : [ "CVE-2026-8139" ],
  "summary" : "Concrete CMS is vulnerable to Stored XSS via external-link page cvName",
  "details" : "Concrete CMS 9.5.0 and below is vulnerable to Stored XSS via external-link page cvName because updateCollectionAliasExternal bypasses being sanitized.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "concrete5/concrete5"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "9.5.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-8139"
  }, {
    "type" : "WEB",
    "url" : "https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/concretecms/concretecms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-24T21:06:04Z",
    "nvd_published_at" : "2026-05-21T22:16:49Z"
  }
}