{"id":"CVE-2026-31833","aliases":["GHSA-vrqc-59mw-qqg7"],"url":"https://o3.security/vulnerability/CVE-2026-31833","summary":"Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering","details":"### Description\nAn 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.\n\n### Impact\nAs 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.\n\n### Patches\nThe issue is patched in 16.5.1 and 17.2.2.\n\n### Workarounds\nThere is no workaround other than upgrading.\n\n### References\nhttps://docs.umbraco.com/umbraco-cms/reference/umbraco-flavored-markdown","published":"2026-03-10T21:51:51.407Z","modified":"2026-08-12T03:51:34.991574486Z","cvss":{"score":6.7,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"Umbraco.Cms","fixedVersion":"16.5.1"},{"ecosystem":"NuGet","name":"Umbraco.Cms","fixedVersion":"17.2.2"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31833.json"},{"type":"ADVISORY","url":"https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-vrqc-59mw-qqg7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31833"},{"type":"PACKAGE","url":"https://github.com/umbraco/Umbraco-CMS"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:34.991574486Z"}}