How severe is CVE-2026-9549?

CVE-2026-9549 has a CVSS 3.x base score of 4.8, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-9549 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-9549?

CVE-2026-9549 primarily affects Checkmk. In total, 157 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-9549?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-9549 have an EU (EUVD) identifier?

Yes. CVE-2026-9549 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-35054.

When was CVE-2026-9549 published?

CVE-2026-9549 was published on 2026-06-08 and last updated on 2026-06-17.

CVE-2026-9549

CVE-2026-9549 is a medium-severity vulnerability in Checkmk with a CVSS 3.x base score of 4.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 4.8)
CVSS v4: 4.8
EPSS exploit prediction: 0% (4th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-35054
Weakness: CWE-79
Affected product: Checkmk
Published: 2026-06-08
Last modified: 2026-06-17

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.

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.
How severe is CVE-2026-9549?: CVE-2026-9549 has a CVSS 3.x base score of 4.8, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-9549 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-9549?: CVE-2026-9549 primarily affects Checkmk. In total, 157 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-9549?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-9549 have an EU (EUVD) identifier?: Yes. CVE-2026-9549 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-35054.
When was CVE-2026-9549 published?: CVE-2026-9549 was published on 2026-06-08 and last updated on 2026-06-17.

References

https://checkmk.com/werk/17993

Affected products (157)

cpe:2.3:a:checkmk:checkmk:2.2.0:-:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b1:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b2:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b3:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b4:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b5:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b6:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b7:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:b8:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:i1:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p1:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p10:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p11:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p12:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p13:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p14:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p15:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p16:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p17:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p18:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p19:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p2:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p20:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p21:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p22:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p23:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p24:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p25:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p26:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p27:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p28:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p29:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p3:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p30:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p31:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p32:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p33:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p34:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p35:*:*:*:*:*:*
cpe:2.3:a:checkmk:checkmk:2.2.0:p36:*:*:*:*:*:*

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