dbcve.org
CheckmkApplication

CVE-2026-8833

MEDIUM · 5.4 CVSS v3.1 Published 2026-06-08
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
58/100
Remediation priority · Elevated
Remotely reachable

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Cross-site scripting (XSS) vulnerability in Checkmk's URL validation function. An authenticated attacker can inject malicious URLs (e.g., javascript: URIs) by bypassing improper HTML-encoded character neutralization, leading to stored XSS when other users interact with crafted links.

MitigationUpgrade Checkmk to version 2.5.0p5, 2.4.0p31, 2.3.0p48, or later to receive the patched URL validation function.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
CheckmkApplication
Affected:= 2.2.0= 2.3.0= 2.4.0= 2.5.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Checkmk version
    Run command: omd version or check the Checkmk web interface under 'Help > About' to view the exact version number
    Affected if The installed version matches 2.2.0, 2.3.0, 2.4.0, or 2.5.0 (or falls within the affected version range)
  2. Locate URL validation configuration
    Navigate to Checkmk setup menu, look for 'URL validation' or 'Link validation' settings under global configuration or notification settings
    Affected if URL validation feature is configured and enabled in the Checkmk environment
  3. Inspect URL validation rules
    Examine the URL validation rule definitions stored in ~/etc/checkmk/multisite.d/wato/ or via the web interface to see what URI schemes are allowed
    Affected if The validation rules permit javascript: or other dangerous URI schemes to pass through
  4. Review notification or dashboard configurations
    Check any custom notification rules or dashboard elements that accept URL inputs for stored links and references
    Affected if User-supplied URLs are being stored and rendered in the Checkmk interface

You are likely affected if your Checkmk version is 2.2.0, 2.3.0, 2.4.0, or 2.5.0 and the URL validation feature is actively used to process user-supplied URLs.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Checkmk to version 2.5.0p5, 2.4.0p31, 2.3.0p48, or later to receive the patched URL validation function.

Recommended fix High confidence

Upgrade to 2.5.0p5 (or later 2.5.x), 2.4.0p31 (or later 2.4.x), or 2.3.0p48 (or later 2.3.x). For 2.2.x users, migrate to a supported branch.

  1. 1. Identify the currently installed Checkmk version using 'cmk --version' or the Checkmk web interface.
  2. 2. Based on the current version branch, upgrade to the corresponding fixed patch release: For 2.5.x versions, upgrade to 2.5.0p5 or later. For 2.4.x versions, upgrade to 2.4.0p31 or later. For 2.3.x versions, upgrade to 2.3.0p48 or later. For 2.2.x versions, upgrade to a newer branch (2.3.x, 2.4.x, or 2.5.x) as no patch is available for 2.2.x.
  3. 3. Follow the standard Checkmk upgrade documentation for your deployment method (package-based or container-based).
  4. 4. After upgrade, verify the URL validation function is properly neutralizing HTML-encoded characters and javascript: URIs are blocked.
  5. 5. Test that the XSS vulnerability is no longer exploitable by attempting to inject a javascript: URI in the URL validation function.
Caveat Patch releases typically contain only bug and security fixes with no breaking changes; however, always review the Checkmk changelog before upgrading.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Checkmk Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-8833 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-8833 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data