CVE-2026-19135 The OpenNMS Group CVE debrief

Who should care

Defenders responsible for OpenNMS Meridian and Horizon installations should assess exposure and prioritize upgrades to prevent potential information disclosure and integrity compromise.

Why it matters

Defenders should prioritize upgrading vulnerable OpenNMS Meridian and Horizon installations to prevent potential information disclosure and integrity compromise. The vulnerability allows a low-privileged authenticated user to submit a crafted JEXL expression to the Measurements REST API, potentially escaping the sandbox and loading arbitrary Java classes on the server. Additional information on exploitation and impact is limited, and defenders should verify vulnerability presence and remediation.

• Potential information disclosure
• Potential integrity compromise
• Verification of vulnerability presence and remediation

Technical summary

A low-privileged authenticated user can submit a crafted JEXL expression to the Measurements REST API in OpenNMS Meridian and Horizon, potentially allowing access to confidential information and compromising integrity. The vulnerability allows a low-privileged authenticated user to escape the sandbox and load arbitrary Java classes on the server. The solution is to upgrade to Meridian 2024.3.12, 2025.0.9, and Horizon 36.0.3 or newer. Defenders should prioritize upgrading vulnerable OpenNMS Meridian and Horizon installations to prevent potential information disclosure and integrity compromise.

Defensive priority

Defenders should prioritize upgrading vulnerable OpenNMS Meridian and Horizon installations to prevent potential information disclosure and integrity compromise.

Recommended defensive actions

• Upgrade OpenNMS Meridian to 2024.3.12 or 2025.0.9
• Upgrade OpenNMS Horizon to 36.0.3
• Restrict access to the Measurements REST API
• Monitor for suspicious activity
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but additional information on exploitation and impact is limited. Defenders should verify vulnerability presence and remediation. The source detail is limited, so defenders should exercise caution and verify the information with other sources. The CVE record was published on 2026-08-13T05:17:22.750Z and has not been modified since then.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.