XSS in Checkmk
CVE-2025-64999
Improper neutralization of input in Checkmk versions 2.4.0 before 2.4.0p22, and 2.3.0 before 2.3.0p43 allows an attacker that can manipulate a host's check output to inject malicious JavaScript into the Synthetic Monitoring HTML logs, which can then be accessed via a crafted phishing link.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.001 (3.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 3rd percentile — 3.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: +0.000
Affected products
- Checkmk — versions 2.3.0, 2.4.0
- Checkmk Gmbh — versions 2.4.0, 2.3.0
Weakness classification (CWE)
References
- checkmk.com/werk/19238 (vendor-advisory, Vendor Advisory)
- github.com/sbaresearch/advisories/tree/e72ce9bb6b9ffffc1fc35e4d8152ad153293c851… (third-party-advisory)
Frequently asked questions
- What is CVE-2025-64999?
- CVE-2025-64999 is a medium-severity vulnerability in Checkmk, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-02-26.
- How severe is CVE-2025-64999?
- Medium severity. CVSS v3 base score is 5.4 out of 10.