CVE-2026-127235
Received Received - Intake

Reflected XSS in OpenNMS Meridian and Horizon

Publication date: 2026-11-12

Last updated on: 2026-11-12

Assigner: The OpenNMS Group

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.

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Meta Information

Published
2026-11-12
Last Modified
2026-11-12
Generated
2026-11-12
AI Q&A
2026-11-12
EPSS Evaluated
N/A
NVD
CVE-2026-127235
EUVD
EUVD-2026-124614

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
The OpenNMS Group Meridian From 2024.1.0 (inc) to 2024.3.15 (exc)
The OpenNMS Group Meridian From 2025.0.0 (inc) to 2025.0.12 (exc)
The OpenNMS Group Meridian From 2026.0.0 (inc) to 2026.0.2 (exc)
The OpenNMS Group Horizon From 36.0.0 (inc) to 36.0.6 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

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Executive Summary

This is a reflected cross-site scripting (XSS) vulnerability in the OpenNMS web user interface. It occurs because several web UI pages copy request parameter values into HTML responses without proper encoding. An attacker can craft a malicious link that executes arbitrary JavaScript in the victim's browser when opened, leveraging the victim's authenticated session to read data or send requests.

Detection Guidance

Detecting this vulnerability requires checking the OpenNMS version. Use commands like 'opennms -v' or check the web UI version in the footer. If the version is below Meridian 2024.3.15, 2025.0.12, 2026.0.2 or Horizon 36.0.6, the system is vulnerable.

Impact Analysis

An attacker could steal session cookies, access sensitive data, or perform actions on your behalf within OpenNMS. Since the script runs in your browser with your session, it may allow unauthorized data access or manipulation. The impact depends on your OpenNMS permissions and the data exposed in the UI.

Compliance Impact

This vulnerability could lead to unauthorized data access or exfiltration, violating confidentiality requirements in GDPR and HIPAA. If exploited, it may result in data breaches, triggering compliance violations, regulatory fines, or reputational damage depending on the exposed data.

Mitigation Strategies

Upgrade OpenNMS to Meridian 2024.3.15, 2025.0.12, 2026.0.2 or Horizon 36.0.6 or newer. Ensure the system is not directly accessible from the Internet as per installation instructions.

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