CVE-2026-127235

OpenNMS reflected cross-site scripting in the web UI via request parameters

Published Nov 12, 2026 CVSS 3.1 · 6.1 Medium EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Solution

Upgrade to Meridian 2024.3.15, 2025.0.12, 2026.0.2 and Horizon 36.0.6 or newer.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Opennms
Opennms horizon
Opennms meridian
The Opennms Group
The Opennms Group horizon
The Opennms Group meridian
Vendors & Products Opennms
Opennms horizon
Opennms meridian
The Opennms Group
The Opennms Group horizon
The Opennms Group meridian
Type Values Removed Values Added
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.
Title OpenNMS reflected cross-site scripting in the web UI via request parameters
Weaknesses CWE-79
References
Metrics cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
OpenNMS
Published
Updated
Nov 12, 2026, 6:06 PM
Reserved
Nov 12, 2026, 5:14 PM
Status
Awaiting Analysis
Published
Nov 12, 2026, 7:17 PM
Modified
Nov 12, 2026, 9:35 PM