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7.3
Checkmk: Malicious JavaScript injection in Synthetic Monitoring logs
CVE-2025-64999
Summary
Checkmk's Synthetic Monitoring logs can be manipulated to inject malicious JavaScript, which can be used to trick users into visiting a phishing website. This only affects Checkmk versions 2.4.0 before 2.4.0p22 and 2.3.0 before 2.3.0p43. Update to a fixed version to prevent this vulnerability.
What to do
No fix is available yet. Check with your software vendor for updates.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.3.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
| checkmk | checkmk | 2.4.0 | – |
Original title
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 int...
Original description
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.
nvd CVSS3.1
5.4
nvd CVSS4.0
7.3
Vulnerability type
CWE-79
Cross-site Scripting (XSS)
Published: 26 Feb 2026 · Updated: 12 Mar 2026 · First seen: 6 Mar 2026