🛡️ CVE-2026-31833 — umbraco-cms

🟡 CVSS 6.7 — Medium ✅ No Known Exploit CWE-79 NVD
6.7
CVSS Score
0 Low4 Medium7 High9 Critical10

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

github.com

Details

Severity MEDIUM
CVSS Score 6.7
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L
CWE CWE-79
Public Exploit ✅ No
Source NVD
Published 2026-03-10
Updated 2026-08-12
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
umbraco-cms 17.0.0 17.2.2
umbraco.cms 17.0.0 17.2.2

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