CVE-2026-19135: OpenNMS JEXL sandbox bypass in Measurements REST API allows ROLE_USER to load arbitrary classes

Vulnerability summary

CVE-2026-19135 is a medium (CVSS 5.4) Unsafe Reflection vulnerability in the opennms group horizon. EPSS estimates a 0.29% chance of exploitation in the next 30 days, higher than 20.2% of scored vulnerabilities.

Timeline

1. 13-08-2026
   PublishedVulnerability first disclosed.
2. 13-08-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-470Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')The product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.