TYPO3-EXT-SA-2021-012: Cross Site Scripting in Extension "Yoast SEO for TYPO3" (yoast_seo)

Categories: Development, Security Created by Torben Hansen
It has been discovered that the extension "Yoast SEO for TYPO3" (yoast_seo) is susceptible to Cross Site Scripting.
  • Release Date: August 10, 2021
  • Component Type: Third party extension. This extension is not a part of the TYPO3 default installation.
  • Component: "Yoast SEO for TYPO3" (yoast_seo)
  • Vulnerability Type: Cross Site Scripting
  • Affected Versions: 7.2.2 and below
  • Severity: Medium
  • Suggested CVSS: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N/E:F/RL:O/RC:C
  • References: CVE-2021-36788

Problem Description

The extension fails to properly encode user input for output in HTML context. A TYPO3 backend user account is required to exploit the vulnerability.


An updated version 7.2.3 is available from the TYPO3 extension manager, Packagist and at
Users of the extension are advised to update the extension as soon as possible.


Thanks to Richie Lee and Security Team Member Oliver Hader for reporting the issues and to Yoast BV for providing an updated version of the extension.

General Advice

Follow the recommendations that are given in the TYPO3 Security Guide. Please subscribe to the typo3-announce mailing list.