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Medium severity · published Mar 10, 2026
CVE-2026-31833
Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering
6.7
CVSS
0.3%
EPSS
No
On KEV
Description
Umbraco is an ASP.NET CMS. From 16.2.0 to before 16.5.1 and 17.2.2, 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. This vulnerability is fixed in 16.5.1 and 17.2.2.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L
Attack vector
Network
Complexity
Low
Privileges
High
User interaction
None
Confidentiality
High
Integrity
High
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
UM
Umbraco-CMS · umbraco
>= 16.2.0, < 16.5.1; >= 17.0.0, < 17.2.1 · source: vendor
UC
Umbraco Cms · Umbraco
16.2.0 before 16.5.1; 17.0.0 before 17.2.2 · source: NVD
Affected product
UM
Umbraco-CMS
umbraco
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-31833
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-31833
Vendor Advisory
https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-vrqc-59mw-qqg7
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