umbraco/umbraco-cms · Security
Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering
- GHSA ID
- GHSA-vrqc-59mw-qqg7
- CVE ID
- CVE-2026-31833
- Severity
- medium
- Published
- Updated
- CVSS
- 6.7 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L
- CVSS v3
- 6.7 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L
Description
Description
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.
Impact
As property type descriptions support Markdown/HTML via the UFM rendering pipeline, injected event handlers are rendered in the backoffice interface, resulting in a stored XSS affecting other backoffice users.
Patches
The issue is patched in 16.5.1 and 17.2.2.
Workarounds
There is no workaround other than upgrading.
References
https://docs.umbraco.com/umbraco-cms/reference/umbraco-flavored-markdown
CWEs
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')