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.NET
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Not in CISA KEV
MEDIUM severity

Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute FilteringGHSA-vrqc-59mw-qqg7

MEDIUM

GHSA-vrqc-59mw-qqg7 is a medium-severity (CVSS 6.7) Cross-site Scripting (XSS) vulnerability in Umbraco.Cms. A fix is available for Umbraco.Cms — see the affected versions and patch details below.

Also known asCVE-2026-31833
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-vrqc-59mw-qqg7.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk+0.03%
Lower risk than most CVEs23th percentile — riskier than 23% of all scored CVEsHighest risk
0.00%0.32%0.64%0.95%0.1%0.3%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected
.NETUmbraco.Cms.NETUmbraco.Cms

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

Description

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 Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
.NETNuGetUmbraco.Cms≥ 16.2.0&&< 16.5.116.5.1dotnet add package Umbraco.Cms --version 16.5.1
.NETNuGetUmbraco.Cms≥ 17.0.0&&< 17.2.217.2.2dotnet add package Umbraco.Cms --version 17.2.2

Affected Products

1 product · 2 configurations
Application
umbraco cmsumbraco
≥ 17.0.0 && < 17.2.2
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Umbraco.Cms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update Umbraco.Cms to 16.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-vrqc-59mw-qqg7 is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### 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. ###
O3 Security · Impact-Aware SCA

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