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.

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)

EPSS: 0.001 (3.9th percentile) — read the EPSS interpretation.

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.

Affected products

Checkmk — versions 2.3.0, 2.4.0
Checkmk Gmbh — versions 2.4.0, 2.3.0

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

security@checkmk.com (vendor-advisory, Vendor Advisory)
security@checkmk.com (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.