Answer in brief
CVE-2026-127235 records a Medium severity (CVSS 6.1) vulnerability in OpenNMS reflected cross-site scripting in the web UI via request parameters. The current sources do not mark it as known exploited. The current feed maps The OpenNMS Group/Horizon (generic), The OpenNMS Group/Meridian (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps The OpenNMS Group/Horizon (generic), The OpenNMS Group/Meridian (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| The OpenNMS Group/Horizongeneric | >=36.0.0 <36.0.6 | 36.0.6 |
| The OpenNMS Group/Meridiangeneric | >=2024.1.0 <2024.3.15 || >=2025.0.0 <2025.0.12 || >=2026.0.0 <2026.0.2 | 2024.3.15, 2025.0.12, 2026.0.2 |
Published upstream
Nov 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Nov 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Nov 12, 2026
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.
Quoted source text, attributed separately from HOL analysis.