# CVE-2026-12199: Unauthenticated Denial of Service in nltk.app.wordnet_app

> Unauthenticated attackers can remotely shut down the local WordNet Browser HTTP server by sending a specific GET request, causing a denial of service.

- **Severity:** High 7.5 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 17 Jun 2026
- **Updated:** 17 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-12199, GHSA-7jvr-hv34-f3rw, UBUNTU-CVE-2026-12199

## What is CVE-2026-12199?

CVE-2026-12199 is a high-severity denial of service vulnerability in nltk/nltk, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in `nltk.app.wordnet_app` up to version 3.9.3 allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when started in its default mode. The server listens on all interfaces and processes a specific unauthenticated GET request (`/SHUTDOWN%20THE%20SERVER`) to terminate the process immediately via `os._exit(0)`. This results in a denial of service, impacting service availability. The issue arises due to insufficient authentication and protection mechanisms for critical server functions.

Weakness: CWE-306 (Missing Authentication for Critical Functionality)

## Which versions are affected by CVE-2026-12199?


## How do I fix CVE-2026-12199?

No fix has been published for CVE-2026-12199 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-12199 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12199 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12199 and fix it if it is affected.

What it is: CVE-2026-12199 is a high-severity denial of service vulnerability in nltk/nltk, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12199 exists.

Affected product: nltk/nltk. 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-2026-12199/ (Markdown: https://insights.sbomify.com/CVE-2026-12199/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12199
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12199
- OSV: https://osv.dev/vulnerability/CVE-2026-12199

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-12199/
Summaries are generated and may contain mistakes; the official description above is the record.