What is CVE-2026-20915?

CVE-2026-20915 is a medium-severity vulnerability in Checkmk, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-03-31.

How severe is CVE-2026-20915?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in Checkmk

CVE-2026-20915

Stored cross-site scripting (XSS) in Checkmk version 2.5.0 (beta) before 2.5.0b2 allows authenticated users with permission to create pending changes to inject malicious JavaScript into the Pending Changes sidebar, which will execute in the browsers of other users viewing the sidebar.

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.001 (4.4th 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 2.5.0
Checkmk Gmbh — versions 2.5.0b1

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

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

Frequently asked questions

What is CVE-2026-20915?: CVE-2026-20915 is a medium-severity vulnerability in Checkmk, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-03-31.
How severe is CVE-2026-20915?: Medium severity. CVSS v3 base score is 5.4 out of 10.