CVE-2026-19182: The Opennms Group Horizon

Medium severity, CVSS 4.3. EPSS: 0.3% chance of exploitation in the next 30 days.

An incorrect authorization check in the v2 Alarm REST API in OpenNMS Meridian and Horizon allows a low-privileged authenticated user (ROLE_REST) to acknowledge, escalate, or clear alarms recorded as an arbitrary username, and, when also assigned ROLE_READONLY, to modify alarm state despite the read-only restriction. A credential check that should restrict these operations is guarded by an inverted condition, so it never executes for a real (non-blank) username. This can potentially allow an attacker to compromise the integrity of alarm state and audit records. 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.