OpenNMS Group Meridian/Horizon REST API authorization

Summaryinfo

A vulnerability categorized as critical has been discovered in OpenNMS Group Meridian and Horizon. Impacted is an unknown function of the component REST API. The manipulation results in authorization. This vulnerability is identified as CVE-2026-111235. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability classified as critical has been found in OpenNMS Group Meridian and Horizon (affected version unknown). Affected is an unknown functionality of the component REST API. The manipulation with an unknown input leads to a authorization vulnerability. CWE is classifying the issue as CWE-639. The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-111235 since 10/15/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 10/15/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• OpenNMS Group

Name

• Horizon
• Meridian

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