CVE-2026-31833
HTML Injection in Umbraco Backoffice via Improper DOMPurify Filtering
Publication date: 2026-03-10
Last updated on: 2026-03-18
Assigner: GitHub, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| umbraco | umbraco_cms | From 17.0.0 (inc) to 17.2.2 (exc) |
| umbraco | umbraco_cms | From 16.2.0 (inc) to 16.5.1 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-79 | The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
This vulnerability exists in Umbraco, an ASP.NET CMS, in versions 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. The root cause is an overly permissive attributeNameCheck configuration (/.+/) in the UFM DOMPurify instance, which fails to filter event handler attributes such as onclick and onload within Umbraco web components (umb-*, uui-*, ufm-*). This allows malicious scripts to be injected and potentially executed.
How can this vulnerability impact me? :
The vulnerability can lead to the injection and execution of malicious HTML and scripts by an authenticated backoffice user. This can result in unauthorized actions being performed, data compromise, or other malicious activities within the Umbraco CMS environment. The CVSS score indicates a high impact on confidentiality and integrity, with some impact on availability.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
I don't know
What immediate steps should I take to mitigate this vulnerability?
To mitigate this vulnerability, you should upgrade Umbraco to version 16.5.1 or 17.2.2 or later, where the issue has been fixed.