# CVE-2026-127235: OpenNMS reflected cross-site scripting in the web UI via request parameters

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

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

- fix: Upgrade to Meridian 2024.3.15, 2025.0.12, 2026.0.2 and Horizon 36.0.6 or newer. (source: CNA: OpenNMS)
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: OpenNMS) — https://github.com/OpenNMS/opennms/pull/9066

## Affected products and versions

- The OpenNMS Group / Meridian: ≥ 2024.1.0; < 2024.3.15 (affected, maven); ≥ 2025.0.0; < 2025.0.12 (affected, maven); ≥ 2026.0.0; < 2026.0.2 (affected, maven). Source: CNA: OpenNMS
- The OpenNMS Group / Horizon: ≥ 36.0.0; < 36.0.6 (affected, maven). Source: CNA: OpenNMS

## Severity and prioritization

- CVSS 3.1: 6.1 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N; source: CNA: OpenNMS

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-79

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/OpenNMS/opennms/pull/9066 (CNA: OpenNMS; patch)

## Provenance

- CNA: OpenNMS: https://www.cve.org/CVERecord?id=CVE-2026-127235; retrieved 2026-11-12; source updated 2026-11-12

Revision: 3725180501197e148dd6a27dfe5ddda3adea5dc02b57ff1d723ff1c86d282055

Canonical: https://y2.dev/cve/CVE-2026-127235

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