XSS in Checkmk
CVE-2025-39663
Cross-Site Scripting (XSS) vulnerability in Checkmk's distributed monitoring allows a compromised remote site to inject malicious HTML code into service outputs in the central site. Affecting Checkmk before 2.4.0p14, 2.3.0p39, 2.2.0 and 2.1.0 (eol).
EPSS: 0.006 (43.5th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.4 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H.
Affected products
- Checkmk — versions 2.3.0, 2.4.0
- Checkmk Gmbh — versions 2.4.0, 2.3.0, 2.2.0
Weakness classification (CWE)
References
- security@checkmk.com (Vendor Advisory)
- security@checkmk.com (Exploit, Third Party Advisory)
- af854a3a-2127-422b-91ae-364da2661108 (Exploit, Mailing List, Third Party Advisory)
Frequently asked questions
- What is CVE-2025-39663?
- CVE-2025-39663 is a high-severity vulnerability in Checkmk, classified under Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). CVSS score: 8.4/10. Published 2025-10-30.
- How severe is CVE-2025-39663?
- High severity. CVSS v3 base score is 8.4 out of 10.