CVE-2020-5809: Umbraco CMS

Medium severity, CVSS 5.4. EPSS: 0.7% chance of exploitation in the next 30 days.

A stored XSS vulnerability exists in Umbraco CMS <= 8.9.1 or current. An authenticated user can inject arbitrary JavaScript code into iframes when editing content using the TinyMCE rich-text editor, as TinyMCE is configured to allow iframes by default in Umbraco CMS.

Affected products

• Umbraco Umbraco CMS: up to and including 8.9.1

Published 2020-12-30. Last modified 2026-06-17.