CVE-2026-127235

Description

A reflected cross-site scripting vulnerability exists in the web user interface of multiple versions of OpenNMS Meridian and Horizon. Several web UI pages copy request parameter values into the HTML response without correct contextual output encoding. A remote attacker can craft a link that runs arbitrary JavaScript in the OpenNMS origin when an authenticated user opens it. The script runs in the victim's browser with the victim's session, so the attacker can read page data and send same-origin requests as the victim. The fix encodes the affected request values. On pages that use AngularJS, the fix also stops client-side template evaluation of the reflected values. The solution is to upgrade to Meridian 2024.3.15, 2025.0.12, 2026.0.2 and Horizon 36.0.6 or newer. Meridian and Horizon installation instructions state that they are intended for installation within an organization's private networks and should not be directly accessible from the Internet.

Severity scores

Each score is shown as its source gave it. They are not averaged or merged.

• 6.1CVSS 3.1, Mediumfrom the CNA (OpenNMS)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

What to do

• Upgrade to Meridian 2024.3.15, 2025.0.12, 2026.0.2 and Horizon 36.0.6 or newer.CNA solution statement

Historical context and remediation

This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.

No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.

Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.

Read the original CVE record.

Affected products

Timeline

1. 12 Nov 2026 Published

Weakness

• CWE-79

References

• github.compatch