CVE-2026-31833Network attack vector

Stored XSS via permissive DOMPurify attribute filtering

Published Mar 10, 2026 · Updated Mar 10, 2026

Stored XSS in Umbraco CMS 16.2.0 through 16.5.0 and 17.0.0 through 17.2.0 allows remote authenticated users to run script. The UFM DOMPurify instance accepts every attribute name, so event handlers on umb-, uui-, and ufm-prefixed web components survive sanitization. An attacker needs backoffice Settings access to save a crafted property type description; rendering it executes script in other backoffice users' sessions.

CVSS severity6.7
Medium
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Umbraco CMS 16.2.0 through 16.5.0 and 17.0.0 through 17.2.0 allows remote authenticated users to run script. The UFM DOMPurify instance accepts every attribute name, so event handlers on umb-, uui-, and ufm-prefixed web components survive sanitization. An attacker needs backoffice Settings access to save a crafted property type description; rendering it executes script in other backoffice users' sessions.

The record

CVE
CVE-2026-31833
Published
Mar 10, 2026
Updated
Mar 10, 2026
Vendor
Umbraco
Product
Umbraco CMS
Classifications
CWE-79, T1203
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Mar 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 16.2.0, < 16.5.1
  2. Affected versionversion=>= 17.0.0, < 17.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Umbraco · Umbraco CMSversion=>= 16.2.0, < 16.5.1; version=>= 17.0.0, < 17.2.1

Published CVSS scores

6.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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