# CVE-2026-111252: OpenNMS denial of service via XML entity expansion

> An authenticated user can cause denial of service in OpenNMS by submitting XML with excessive entity expansion, exhausting server memory.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Oct 2026
- **Updated:** 16 Oct 2026
- **Also known as:** GHSA-vc8g-329j-xw8w

## What is CVE-2026-111252?

CVE-2026-111252 is a medium-severity vulnerability in The OpenNMS Group Horizon, published on 15 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A denial of service vulnerability exists in the XML parsing of multiple versions of OpenNMS Meridian and Horizon. OpenNMS parsed XML without an effective limit on entity expansion. A document with a DOCTYPE that declares internal entities can expand to a very large value and exhaust the server memory. An authenticated user with provisioning access can supply such a document through a requisition or foreign-source import, which includes a remote requisition URL that the server fetches and parses. Both deeply nested entities and a single large entity referenced many times cause the memory exhaustion. The fix caps the number of entity expansions for all XML parsing and rejects any DOCTYPE in requisition and foreign-source XML.

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.

Weakness: CWE-776 (Improper Restriction of Recursive Entity References in DTDs), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-111252?


## How do I fix CVE-2026-111252?

No fix has been published for CVE-2026-111252 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-111252 being exploited?

There is no known exploitation of CVE-2026-111252 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-111252 and fix it if it is affected.

What it is: CVE-2026-111252 is a medium-severity vulnerability in The OpenNMS Group Horizon, published on 15 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-111252 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-2026-111252/ (Markdown: https://insights.sbomify.com/CVE-2026-111252/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-111252
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-111252
- OSV: https://osv.dev/vulnerability/CVE-2026-111252

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-111252/
Summaries are generated and may contain mistakes; the official description above is the record.