CVE-2026-31833

Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering

State: Published
Severity: 6.7 Medium
Published: Mar 10, 2026
Updated: Mar 11, 2026
Reserved: Mar 9, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	6.7 Medium	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L	GitHub_M

Weaknesses

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Affected Products

Product	Versions
Umbraco-CMSumbraco	>= 16.2.0, < 16.5.1Affected >= 17.0.0, < 17.2.1Affected

References

https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-vrqc-59mw-qqg7

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