XSS in Checkmk
CVE-2026-9549
Stored cross-site scripting in the service discovery active check output in Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions allows an administrator who can configure active or custom checks to inject malicious HTML or JavaScript into check output that executes in the browser of an admin or a user with host read permissions when they run the check on the service discovery page.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.001 (3.8th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N.
Affected products
- Checkmk — versions 2.2.0, 2.3.0, 2.4.0
- Checkmk Gmbh — versions 2.5.0, 2.4.0, 2.3.0
Weakness classification (CWE)
References
- security@checkmk.com (vendor-advisory, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-9549?
- CVE-2026-9549 is a medium-severity vulnerability in Checkmk, classified under Cross-site Scripting. CVSS score: 4.8/10. Published 2026-06-08.
- How severe is CVE-2026-9549?
- Medium severity. CVSS v3 base score is 4.8 out of 10.