Uptime Kuma's Matomo analytics integration (server/analytics/matomo-analytics.js) injects the...

Uptime Kuma's Matomo analytics integration (server/analytics/matomo-analytics.js) injects the admin-configurable Matomo siteId value as a bare, unquoted JavaScript expression inside a block rendered on every public status page: _paq.push(['setSiteId', ${escapedSiteIdHTMLAttribute}]);. The escaping pipeline used (jsesc with isScriptContext:true, then html-escaper.escape()) does not escape the characters ], ), ;, (, which are sufficient to break out of the array/push expression context. A siteId value such as 1]);alert(document.cookie)//, once saved by an editor/admin, executes arbitrary JavaScript for every unauthenticated visitor of the public /status/ page, enabling session-cookie theft and full page takeover.