CVE-2026-71285: XSS (CVSS 8.1)

Description

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 <script> 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/<slug> page, enabling session-cookie theft and full page takeover.

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CVSS v3.1 Score

8.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:N

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

References

Other References

https://github.com/louislam/uptime-kuma https://github.com/louislam/uptime-kuma/blob/master/server/analytics/matomo-analytics.js

Frequently Asked Questions

What is CVE-2026-71285? +

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 <script> 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/<slug> page, enabling session-cookie theft and full page takeover. It has a CVSS v3.1 base score of 8.1 (HIGH).

How severe is CVE-2026-71285? +

CVE-2026-71285 has a CVSS v3.1 score of 8.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

How do I check if I'm vulnerable to CVE-2026-71285? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-71285