CVE-2025-39663: Checkmk

High severity, CVSS 8.4. EPSS: 0.6% chance of exploitation in the next 30 days.

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).

Affected products

• Checkmk Checkmk: from 2.0.0, before 2.3.0 (fixed in 2.3.0); version 2.3.0 only; version 2.4.0 only

Published 2025-10-30. Last modified 2026-06-17.