| Package | Affected versions | Patched versions |
|---|---|---|
| Umbraco.Cms | ≥ 16.2.0, < 16.5.1≥ 17.0.0, < 17.2.2 | 16.5.117.2.2 |
| umbraco cms | ≥ 16.2.0, < 16.5.1≥ 17.0.0, < 17.2.2 | 16.5.117.2.2 |
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.
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.
The issue is patched in 16.5.1 and 17.2.2.
There is no workaround other than upgrading.
https://docs.umbraco.com/umbraco-cms/reference/umbraco-flavored-markdown
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