What’s Vulnerable › Vulnerabilities
CVE-2026-111235: OpenNMS REST authorization bypass via non-canonical HTTP method
- Severity: critical (CVSS 9.1 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-10-15 · updated 2026-10-16
- Weakness: CWE-204
Description
An authorization bypass vulnerability exists in the REST API of multiple versions of OpenNMS Meridian and Horizon. The /rest/** Spring Security filter chains authorize requests with intercept-url rules that name the HTTP method as an uppercase token, compare the method case-sensitively, and have no terminal deny rule. A request that uses a non-canonical (for example lowercase) method token matches no rule and is processed without authentication. A remote, unauthenticated attacker can read the monitored inventory and can create, modify, or delete resources through the REST API, which includes injecting events to fabricate or suppress alarms. The /rest/alarms chain has the same missing deny rule and discloses whether an alarm exists through a difference in the response. The fix adds a terminal deny rule to each REST filter chain. The solution is to upgrade to Meridian 2024.3.14, 2025.0.11, 2026.0.1 and Horizon 36.0.5 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 36.0.5 — fixed in 36.0.5
- The OpenNMS Group Meridian: from 2024.1.0 before 2024.3.14; from 2025.0.0 before 2025.0.11; from 2026.0.0 before 2026.0.1 — fixed in 2024.3.14, 2025.0.11, 2026.0.1
How to fix
Upgrade to a fixed version: The OpenNMS Group Horizon 36.0.5; The OpenNMS Group Meridian 2024.3.14, 2025.0.11, 2026.0.1. Check the vendor advisory for mitigations.
References
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