Is CVE-2026-9549 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-9549 being exploited in the wild.

How severe is CVE-2026-9549?

Informational severity, with a CVSS score of 4.8, published 8 June 2026.

Which products and versions are affected?

Checkmk GmbH Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, all 2.2.0 versions.

Is there a fix for CVE-2026-9549?

A patch was published on 2026-05-26: Fix released in various versions via Werk #17993 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-9549 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-9549?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-9549: Checkmk stored XSS in service discovery active check output

Q: Is there a fix for CVE-2026-9549?

A patch was published on 2026-05-26: Fix released in various versions via Werk #17993 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-9549 attacked?

It is attacked over the network, in a network appliance.

Q: Am I affected by CVE-2026-9549?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-9549 · Severity: info · CVSS 4.8 · Published 2026-06-08

Checkmk, a popular IT infrastructure monitoring platform, is affected by a security vulnerability in its service discovery component. An administrator with the ability to configure monitoring checks can inject malicious scripts that execute in the browsers of other administrators or authorized users. This could lead to unauthorized actions being performed on behalf of the victim or the theft of sensitive session information.

Quick answers

Is CVE-2026-9549 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-9549 being exploited in the wild.
How severe is CVE-2026-9549?: Informational severity, with a CVSS score of 4.8, published 8 June 2026.
Which products and versions are affected?: Checkmk GmbH Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, all 2.2.0 versions.
Is there a fix for CVE-2026-9549?: A patch was published on 2026-05-26: Fix released in various versions via Werk #17993 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-9549 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-9549?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A stored cross-site scripting (XSS) vulnerability exists in Checkmk due to improper HTML escaping of active or custom check outputs on the service discovery page. When a user clicks 'Run check', the application inserts the check output directly into the DOM without sanitization. An attacker with administrative privileges (required to configure these checks) can store a malicious payload that executes when another administrator or a user with host read permissions triggers the check execution. The vulnerability is addressed in versions 2.5.0p5, 2.4.0p31, and 2.3.0p48.

Affected products

Checkmk GmbH Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, all 2.2.0 versions

Timeline

2026-05-26: patched: Fix released in various versions via Werk #17993
2026-06-08: disclosed: CVE published

References

https://checkmk.com/werk/17993

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