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Vulnerabilities

Security incident · 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

Published Oct 30, 2025 · catalog updated Nov 7, 2025 · Checkmk GmbH Checkmk

Last checked Oct 25, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2025-39663. EPSS is 0.60%. Act only if a listed version of Checkmk GmbH Checkmk is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High8.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.60%
Remediation
Version ranges on file
Affected products
vendor Checkmk GmbH Checkmk 2.4.0 <2.4.0p14

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).

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor Checkmk GmbH Checkmk 2.4.0 <2.4.0p142.4.0 <2.4.0p14

How to fix CVE-2025-39663

  • Upgrade

    CVE-2025-39663 lists a fix boundary at 2.4.0p14. Compare the installed build with that boundary before you change production.

  • Version check

    Seen in 2.4.0 <2.4.0p14

  • Advisory

    Open the cve_org record and follow its fix.

  • Official advisories

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-39663. EPSS is 0.60%. Act only if a listed version of Checkmk GmbH Checkmk is installed.

Which versions are affected?

Compare what you have installed with Checkmk GmbH Checkmk 2.4.0 <2.4.0p14 2.4.0 <2.4.0p14. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.60%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 30, 2025 · EUVD

    Detected

    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).

  2. Nov 7, 2025 · EUVD

    Updated

    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).

Sources

  • CVE.orgVulnerability recordCVE-2025-39663

    Official CVE identifier

    cve.org
  • EUVDVulnerability recordEUVD-2025-36997

    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).

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Oct 25, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • CVE.orgOct 25, 2026
  • EUVDOct 25, 2026