Loading...
Skip to main content
GeekWala

CVE-2026-31833 — Umbraco has Stored XSS in Umbraco.Cms — CVE Details

MEDIUM

Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering

Published March 11, 2026Updated March 13, 2026Source: osv

Summary

### 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

Advisory Timeline

  • First published March 11, 2026 (215 days ago).
  • Last revised March 13, 2026 — 2 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

NuGet
Update Umbraco.Cms to 16.5.1 or later
dotnet add package Umbraco.Cms --version 16.5.1
NuGet
Update Umbraco.Cms to 17.2.2 or later
dotnet add package Umbraco.Cms --version 17.2.2

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (2)

Affects 1 ecosystem: nuget (1).

PackageEcosystemAffectedFixed In
Umbraco.Cms
nuget
16.2.0, 16.3.0, 16.3.0-rc, 16.3.0-rc2 (+12 more)16.5.1
Umbraco.Cms
nuget
17.0.0, 17.0.1, 17.0.2, 17.1.0 (+5 more)17.2.2

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

  • CWE-79
    Cross-site Scripting (XSS)MITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 6.7 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L

References

Frequently Asked Questions

What is CVE-2026-31833?
Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering This vulnerability has been assigned a severity rating of MEDIUM (CVSS score: 6.7/10).
How do I check if my project is affected by CVE-2026-31833?
CVE-2026-31833 affects Umbraco.Cms. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-31833 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
6.7

Exploitation requires specific conditions or has limited impact. Remediate within weeks.

Also Known As

GHSA-vrqc-59mw-qqg7

Related CVEs

Check if you're affected

Scan your dependencies to see if this vulnerability affects your projects.

Scan Your Dependencies