Vulnerability · Published Jun 8, 2026 · Assigned by Checkmk

CVE-2026-9549Fix XSS in service discovery active check output

Medium 4.8

In plain English

A medium-severity cross-site scripting in Checkmk from Checkmk GmbH. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 4% of all known vulnerabilities).

Severity (CVSS 4.0)4.8Medium

Exploit odds (30 days)0.1%top 96.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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.

Affected products (as reported)

Vendor	Product	Versions
Checkmk GmbH	Checkmk	2.5.0 – before 2.5.0p52.4.0 – before 2.4.0p312.3.0 – before 2.3.0p482.2.0

Weakness: CWE-79 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

References

https://checkmk.com/werk/17993 vendor-advisory