CVE-2020-5809

Name: CVE-2020-5809
Creator: NVD / NIST
Published: 2020-12-30T16:15:12.32+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.4/10EPSS 0.68%

Last modified Jun 17, 2026

CVE-2020-5809 is a medium-severity vulnerability rated 5.4/10 on the CVSS scale. 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.. EPSS estimates a 0.68% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

5.4/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

EPSS Probability

0.68%

47.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Umbraco	Umbraco Cms	<= 8.9.1

References

https://www.tenable.com/security/research/tra-2020-59Exploit, Third Party Advisory
https://www.tenable.com/security/research/tra-2020-59Exploit, Third Party Advisory

Timeline

Published: Dec 30, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-5809?

How severe is CVE-2020-5809?

CVE-2020-5809 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 0.68% probability of exploitation in the next 30 days.

How do I fix CVE-2020-5809?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2020-5809?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST