CVE-2026-31833 Details
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.
A stored cross-site scripting vulnerability has been identified in Umbraco CMS versions 16.2.0 prior to 16.5.1 and 17.2.2. This issue allows authenticated backoffice users with access to the Settings section to inject malicious HTML into property type descriptions. The vulnerability arises from an overly permissive attribute name check in the UFM DOMPurify instance, which failed to properly filter event handler attributes like 'onclick' and 'onload' when used within specific Umbraco web components. As a result, injected event handlers are executed in the backoffice interface, potentially affecting other users.
Users can upgrade to Umbraco versions 16.5.1 or 17.2.2 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Mar 11, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-vrqc-59mw-qqg7 | [email protected] | Vendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| umbraco umbraco cms | >= 16.2.0, < 16.5.1 >= 17.0.0, < 17.2.2 |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Mar 18, 2026 | Initial Analysis | [email protected] |
| Mar 10, 2026 | New CVE Received | [email protected] |