🛡️ CVE-2026-31833 — umbraco-cms
Description
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
How this vulnerability can be exploited
This issue can be reached over the network, attack complexity is low, an attacker needs administrative privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability low.
Weakness class
CVE-2026-31833 is classified as CWE-79: Cross-site Scripting (XSS). User-supplied data is written into a page without escaping, so attacker script runs in the browser of anyone who views it.
Affected software
CVE-2026-31833 is recorded against 2 packages.
- umbraco-cms (from 17.0.0 up to 17.2.2)
- umbraco.cms (from 17.0.0 up to 17.2.2)
Timeline and source
Published on 10 March 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.
References
Details
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| umbraco-cms | 17.0.0 | 17.2.2 |
| umbraco.cms | 17.0.0 | 17.2.2 |
References
Similar Threats
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- Medium CVE-2024-43377
More CVE 2026 advisories
Browse all of CVE 2026 in the advisory index.
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