How severe is CVE-2020-5809?

CVE-2020-5809 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2020-5809 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (48th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-5809?

CVE-2020-5809 affects Umbraco Umbraco Cms. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2020-5809?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2020-5809 published?

CVE-2020-5809 was published on 2020-12-30 and last updated on 2026-06-17.

CVE-2020-5809

CVE-2020-5809 is a medium-severity vulnerability in Umbraco Umbraco Cms with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v2: 3.5
EPSS exploit prediction: 1% (48th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Umbraco Umbraco Cms
Published: 2020-12-30
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2020-5809?: 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.
How severe is CVE-2020-5809?: CVE-2020-5809 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2020-5809 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (48th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-5809?: CVE-2020-5809 affects Umbraco Umbraco Cms. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2020-5809?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2020-5809 published?: CVE-2020-5809 was published on 2020-12-30 and last updated on 2026-06-17.

References

https://www.tenable.com/security/research/tra-2020-59

Affected products (1)

cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*

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