CVE-2026-9549 Fix XSS in service discovery active check output
Administrators can inject malicious scripts into service discovery check outputs, which execute in the browsers of other users viewing the page.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-9549?
CVE-2026-9549 is a medium-severity cross-site scripting vulnerability in Checkmk Checkmk, published on 8 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Official description
Stored cross-site scripting in the service discovery active check output in Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions allows an administrator who can configure active or custom checks to inject malicious HTML or JavaScript into check output that executes in the browser of an admin or a user with host read permissions when they run the check on the service discovery page.
Weakness: CWE-79
Which versions are affected by CVE-2026-9549?
It affects 1 product.
Products include Checkmk Checkmk.
How do I fix CVE-2026-9549?
No fix has been published for CVE-2026-9549 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-9549 being exploited?
There is no known exploitation of CVE-2026-9549 in the wild and no public exploit code.
Other vulnerabilities in Checkmk Checkmk
- CVE-2025-39666 omd: Local privilege escalation when executing omd commands as root
- CVE-2024-8606 Fix 2FA bypass via RestAPI
- CVE-2022-46836 PHP code injection in watolib
- CVE-2025-32919 Privilege Escalation in Windows License plugin for Checkmk Windows Agent
- CVE-2024-28827 Privilege escalation in Windows agent
Sources
Also known as GHSA-h7cw-jgmc-mwc6, UBUNTU-CVE-2026-9549.