How severe is CVE-2026-20915?

CVE-2026-20915 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-20915 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-2026-20915?

CVE-2026-20915 affects Checkmk. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-20915?

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

Does CVE-2026-20915 have an EU (EUVD) identifier?

Yes. CVE-2026-20915 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-17417.

When was CVE-2026-20915 published?

CVE-2026-20915 was published on 2026-03-31 and last updated on 2026-06-17.

CVE-2026-20915

CVE-2026-20915 is a medium-severity vulnerability in Checkmk with a CVSS 3.x base score of 5.4. 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 5.4)
CVSS v4: 8.5
EPSS exploit prediction: 0% (4th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-17417
Weakness: CWE-79
Affected product: Checkmk
Published: 2026-03-31
Last modified: 2026-06-17

Description

Stored cross-site scripting (XSS) in Checkmk version 2.5.0 (beta) before 2.5.0b2 allows authenticated users with permission to create pending changes to inject malicious JavaScript into the Pending Changes sidebar, which will execute in the browsers of other users viewing the sidebar.

Frequently asked questions

What is CVE-2026-20915?: Stored cross-site scripting (XSS) in Checkmk version 2.5.0 (beta) before 2.5.0b2 allows authenticated users with permission to create pending changes to inject malicious JavaScript into the Pending Changes sidebar, which will execute in the browsers of other users viewing the sidebar.
How severe is CVE-2026-20915?: CVE-2026-20915 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-20915 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-2026-20915?: CVE-2026-20915 affects Checkmk. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-20915?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-20915 have an EU (EUVD) identifier?: Yes. CVE-2026-20915 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-17417.
When was CVE-2026-20915 published?: CVE-2026-20915 was published on 2026-03-31 and last updated on 2026-06-17.

References

https://checkmk.com/werk/19526

Affected products (1)

cpe:2.3:a:checkmk:checkmk:2.5.0:b1:*:*:*:*:*:*

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