CVE-2026-19135: The Opennms Group Horizon

Medium severity, CVSS 5.4. EPSS: 0.3% chance of exploitation in the next 30 days.

A JEXL expression sandbox bypass exists in multiple versions of OpenNMS Meridian and Horizon. A low-privileged authenticated user can submit a crafted expression to the Measurements REST API that escapes the sandbox and loads arbitrary Java classes on the server. This can potentially allow an attacker to gain access to confidential information and compromise integrity. The solution is to upgrade to Meridian 2024.3.12, 2025.0.9 and Horizon 36.0.3 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.

Affected products

• The Opennms Group Horizon: from 36.0.0, before 36.0.3 (fixed in 36.0.3)
• The Opennms Group Meridian: from 2024.1.0, before 2024.3.12 (fixed in 2024.3.12); from 2025.0.0, before 2025.0.9 (fixed in 2025.0.9)

Published 2026-08-13. Last modified 2026-09-08.