CVE-2020-5809 Umbraco CMS vulnerable to stored XSS

What is CVE-2020-5809?

CVE-2020-5809 is a medium-severity cross-site scripting vulnerability in Umbraco Umbraco Cms, published on 30 Dec 2020. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official description

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.

Weakness: CWE-79

Which versions are affected by CVE-2020-5809?

2 open source packages ship an affected version, including UmbracoCms.Core. It affects 1 product.

Products include Umbraco Umbraco Cms.

How do I fix CVE-2020-5809?

No fix has been published for CVE-2020-5809 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2020-5809 being exploited?

There is no known exploitation of CVE-2020-5809 in the wild and no public exploit code.

Other vulnerabilities in Umbraco Umbraco Cms

• CVE-2025-67288 Umbraco CMS has an arbitrary file upload vulnerability Critical 10.0
• CVE-2014-10074 File upload in n/a Critical 9.8
• CVE-2012-1301 Server-side request forgery in n/a Critical 9.8
• CVE-2012-10054 Umbraco CMS < 4.7.1 codeEditorSave.asmx RCE Critical 9.3
• CVE-2025-32017 Umbraco has a Management API Vulnerability to Path Traversal With Authenticated Users High 8.8

All Umbraco Umbraco Cms vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-95qr-67rx-9pgh.