CVE-2026-9549

MEDIUM
Published Jun 8, 2026 Modified Jun 8, 2026 CWE-79

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.

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CVSS v3.1 Score

4.8
MEDIUM
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0014
Probability of exploitation
0.04%
Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

Affected Products

Vendor Product
checkmk checkmk
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References

Advisories & Patches

https://checkmk.com/werk/17993

Frequently Asked Questions

What is CVE-2026-9549? +
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. It has a CVSS v3.1 base score of 4.8 (MEDIUM).
How severe is CVE-2026-9549? +
CVE-2026-9549 has a CVSS v3.1 score of 4.8 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0014, placing it in the 0th percentile for exploitation probability.
What products are affected by CVE-2026-9549? +
CVE-2026-9549 affects products from checkmk, specifically: checkmk. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2026-9549? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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