XSS in Checkmk
CVE-2026-8833
Improper neutralization of HTML-encoded characters in the URL validation function in Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions allows an authenticated user to bypass URL validation and inject malicious URLs such as javascript: URIs, resulting in cross-site scripting when another user interacts with the crafted 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: 0.002 (14.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
- Checkmk — versions 2.2.0, 2.3.0, 2.4.0
- Checkmk Gmbh — versions 2.5.0, 2.4.0, 2.3.0
Weakness classification (CWE)
References
- checkmk.com/werk/20002 (vendor-advisory, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-8833?
- CVE-2026-8833 is a medium-severity vulnerability in Checkmk, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-06-08.
- How severe is CVE-2026-8833?
- Medium severity. CVSS v3 base score is 5.4 out of 10.