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CVE-2026-8833 Checkmk GmbH CVE debrief

CVE-2026-8833 is a HIGH severity vulnerability in Checkmk versions <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions. It 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.

Vendor
Checkmk GmbH
Product
Checkmk
CVSS
HIGH 8.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-08
Original CVE updated
2026-07-23
Advisory published
2026-06-08
Advisory updated
2026-07-23

Who should care

Users of Checkmk versions <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions should apply patches or mitigations.

Technical summary

The vulnerability is caused by improper neutralization of HTML-encoded characters in the URL validation function. This allows an authenticated user to inject malicious URLs, potentially leading to cross-site scripting (XSS) attacks.

Defensive priority

HIGH

Recommended defensive actions

  • Apply patches or updates to Checkmk versions <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions.
  • Implement additional security measures to monitor and restrict user input.

Evidence notes

CVE-2026-8833 has a CVSS score of 8.5 and is considered HIGH severity. The vulnerability was published on 2026-06-08T13:16:33.900Z and modified on 2026-06-09T14:49:31.967Z.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-8833 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-8833

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-8833 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-8833

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.