Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering
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
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| .NET (NuGet) | Umbraco.Cms | >= 16.2.0, < 16.5.1, >= 17.0.0, < 17.2.2 | 16.5.1, 17.2.2 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L- Weakness (CWE)
CWE-79- Platform
- .NET (NuGet)
- Package
Umbraco.Cms- Disclosed
- 11.03.2026
- Updated
- 11.10.2026 11:23
Sources and licenses
OSV / GitHub Advisory Database - GHSA-vrqc-59mw-qqg7 - CC BY 4.0
Vulnerability history: Umbraco.Cms
All published vulnerabilities of this package (.NET (NuGet)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 29
- First → latest
- 05.2022 09.2026
- Without a fix
- 1
- Exploited in attacks
- 0
Severity breakdown
- High 5
- Medium 17
- Low 7
Disclosures per year
- 2022: 2
- 2023: 8
- 2024: 5
- 2025: 8
- 2026: 6
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Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering this entry
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