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

> An XXE vulnerability in OpenNMS allows attackers to read sensitive files and induce out-of-band requests via malicious XML responses.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 10 Sep 2026
- **Updated:** 10 Sep 2026
- **Also known as:** GHSA-9hqx-g6f2-rj2p

## What is CVE-2026-19596?

CVE-2026-19596 is a medium-severity vulnerability in The OpenNMS Group Horizon, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference)

## Which versions are affected by CVE-2026-19596?


## How do I fix CVE-2026-19596?

No fix has been published for CVE-2026-19596 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-19596 being exploited?

There is no known exploitation of CVE-2026-19596 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19596 and fix it if it is affected.

What it is: CVE-2026-19596 is a medium-severity vulnerability in The OpenNMS Group Horizon, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-19596 in the wild and no public exploit code.

Affected product: The OpenNMS Group Horizon. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-19596/ (Markdown: https://insights.sbomify.com/CVE-2026-19596/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19596
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19596
- OSV: https://osv.dev/vulnerability/CVE-2026-19596

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19596/
Summaries are generated and may contain mistakes; the official description above is the record.