---
id: CVE-2026-81900
title: >-
  Concrete CMS before 9.5.3 applied only trim() to the YouTube block's stored
  width and height values and printed them into iframe HTML attributes without
  escaping or integer casting, resulting in stored cross-site scripting
summary: >-
  Concrete CMS before 9.5.3 applied only trim() to the YouTube block's stored
  width and height values and printed them into iframe HTML attributes without
  escaping or integer casting, resulting in stored cross-site scripting. A user
  with e…
severity: medium
cvss: 6.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'
cwe:
  - CWE-79
vendor: concretecms
product: concrete_cms
affected:
  - concrete_cms < 9.5.3
patched:
  - concrete_cms 9.5.3
published: '2026-09-14'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T20:47:10.650'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-81900'
references:
  - url: >-
      https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes
    label: ff5b8ace-8b95-4078-9743-eac1ca5451de
tags:
  - nvd
  - cve.org
epss: 0.00151
epssPercentile: 0.04598
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-09-15T13:44:15.554567Z'
scores:
  nvd: 6.1
  cna: 7.3
ingestedAt: '2026-09-14T23:17:06.520Z'
---

## Overview

Concrete CMS before 9.5.3 applied only trim() to the YouTube block's stored width and height values and printed them into iframe HTML attributes without escaping or integer casting, resulting in stored cross-site scripting. A user with edit_block permission could inject an event handler that executed script for visitors rendering the page, acting with administrative privileges where the victim was an administrator. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks sh4d0byss for reporting.

## Affected

- `concrete_cms < 9.5.3`

## Remediation

Upgrade past the affected range:

- `concrete_cms 9.5.3`