What is CVE-2026-31833?

CVE-2026-31833 is a medium-severity vulnerability in Umbraco Umbraco-Cms, classified under Cross-site Scripting. CVSS score: 6.7/10. Published 2026-03-10.

How severe is CVE-2026-31833?

Medium severity. CVSS v3 base score is 6.7 out of 10.

XSS in Umbraco Umbraco-Cms

CVE-2026-31833

Umbraco is an ASP.NET CMS. From 16.2.0 to before 16.5.1 and 17.2.2, An authenticated backoffice user with access to Settings can inject malicious HTML into property type descriptions. Due to an overly permissive attributeNameCheck configuration (/.+/) in the UFM DOMPurify instance, event handler attributes such as onclick and onload, when used within Umbraco web components (umb-*, uui-*, ufm-*) were not filtered. This vulnerability is fixed in 16.5.1 and 17.2.2.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-03-10 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.7 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L.

EPSS exploit prediction

EPSS: 0.003 (20.1th percentile), scored 2026-11-03.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 20th percentile — 20.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.003 · change: -0.002

Affected products

Umbraco Umbraco-Cms — versions >= 16.2.0, < 16.5.1, >= 17.0.0, < 17.2.1
Umbraco Cms

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-vrqc-59mw-qqg7 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-31833?: CVE-2026-31833 is a medium-severity vulnerability in Umbraco Umbraco-Cms, classified under Cross-site Scripting. CVSS score: 6.7/10. Published 2026-03-10.
How severe is CVE-2026-31833?: Medium severity. CVSS v3 base score is 6.7 out of 10.