OpenNMS Group Meridian/Horizon v2 Alarm REST API improper authorization

Summaryinfo

A vulnerability marked as critical has been reported in OpenNMS Group Meridian and Horizon. This vulnerability affects unknown code of the component v2 Alarm REST API. Performing a manipulation results in improper authorization. This vulnerability is reported as CVE-2026-19182. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in OpenNMS Group Meridian and Horizon (the affected version is unknown). It has been classified as critical. This affects an unknown code of the component v2 Alarm REST API. The manipulation with an unknown input leads to a improper authorization vulnerability. CWE is classifying the issue as CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-19182 since 08/06/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/13/2026). MITRE ATT&CK project uses the attack technique T1548.002 for this issue.

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

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-57719). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• OpenNMS Group

Name

• Horizon
• Meridian

CPE 2.3info

• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion