Executive brief
OpenNMS Horizon is a network monitoring and alerting system used to track infrastructure health and generate alarms. An unauthenticated attacker who can reach the web interface can disable event definitions and SNMP data collection, silently suppressing alarms and stopping metric collection—degrading the organization's ability to detect and respond to network and system failures.
Technical details
A missing authorization vulnerability exists in OpenNMS Horizon's Spring Security policy for the /api/v2 REST API. The security configuration defines authorization rules for all HTTP methods except PATCH, leaving PATCH endpoints for event configuration and SNMP data collection unprotected. An unauthenticated attacker with network access to the web UI can send PATCH requests to disable event definitions and data-collection sources, with changes persisted to the running system. The vulnerability requires network reachability to the web interface but no authentication. A patch is available in Horizon 36.0.4 and later.
Affected products
- OpenNMS Horizon prior to 36.0.4
Timeline
- 2026-09-10: disclosed: CVE-2026-89054 published
- 2026-09: patched: Fix merged in Horizon 36.0.4