---
id: CVE-2026-18111
title: >-
  Concrete CMS 9 before 9.5.3 was vulnerable to stored cross-site scripting
  (XSS) in the Feature, Feature Link, Hero Image, and Image blocks and before
  Concrete 8.5.21 in the feature and Image blocks because the external link URL
  was insuf…
summary: >-
  Concrete CMS 9 before 9.5.3 was vulnerable to stored cross-site scripting
  (XSS) in the Feature, Feature Link, Hero Image, and Image blocks and before
  Concrete 8.5.21 in the feature and Image blocks because the external link URL
  was insuf…
severity: high
cvss: 8.5
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-306
vendor: Concrete CMS
product: Concrete CMS
affected:
  - concrete_cms >= 9.0.0 <= 9.5.2
published: '2026-09-15'
updated: '2026-09-22'
sourceUpdated: '2026-09-22T19:16:42.030'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-18111'
references:
  - url: >-
      https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes
    label: ff5b8ace-8b95-4078-9743-eac1ca5451de
tags:
  - nvd
  - cve.org
epss: 0.00345
epssPercentile: 0.25203
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-09-22T18:10:12.501642Z'
cvssSource: cna
ingestedAt: '2026-09-15T17:41:02.860Z'
---

## Overview

Concrete CMS 9 before 9.5.3 was vulnerable to stored cross-site scripting (XSS) in the Feature, Feature Link, Hero Image, and Image blocks and before Concrete 8.5.21 in the feature and Image blocks because the external link URL was insufficiently validated by the link filter and was rendered without output escaping. A user with page-editing permissions (such as Add Block combined with Edit Contents on a single page) could store a crafted external link value that broke out of the link markup and injected arbitrary JavaScript. The script executed in the browser session of any user who subsequently viewed, previewed, or edited the affected page, which could lead to session hijacking and escalation of privileges up to full administrative takeover. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 8.5 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks to KhanMarshai for reporting this issue.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.