# CVE-2026-33231: NLTK has unauthenticated remote shutdown in nltk.app.wordnet_app

> An unauthenticated remote attacker can shut down the local WordNet Browser HTTP server by sending a specific GET request, causing a denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/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:** Yes
- **Published:** 20 Mar 2026
- **Updated:** 9 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-33231, ECHO-05d0-935c-6543, GHSA-jm6w-m3j8-898g, MINI-rq22-v2h9-29q3, PYSEC-2026-2236, ROOT-APP-PYPI-CVE-2026-33231

## What is CVE-2026-33231?

CVE-2026-33231 is a high-severity missing authorization vulnerability in nltk, published on 20 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

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

## Which versions are affected by CVE-2026-33231?

3 open source packages ship an affected version, including nltk. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nltk` | PyPI | All versions | 3.9.4 |
| `nltk` | PyPI | All versions | 3.9.4 |
| `nltk` | PyPI | All versions | 3.9.4 |

Products: Nltk Nltk.

## How do I fix CVE-2026-33231?

Upgrade nltk to 3.9.4 or later.

## Is CVE-2026-33231 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33231 exists.

## Other vulnerabilities in nltk

- [CVE-2026-0848](https://insights.sbomify.com/CVE-2026-0848/): Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading (critical 10.0)
- [CVE-2025-14009](https://insights.sbomify.com/CVE-2025-14009/): Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution (critical 10.0)
- [CVE-2026-78683](https://insights.sbomify.com/CVE-2026-78683/): NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization (critical 9.4)
- [CVE-2026-79657](https://insights.sbomify.com/CVE-2026-79657/): NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization (critical 9.3)
- [CVE-2026-79675](https://insights.sbomify.com/CVE-2026-79675/): NLTK before 3.10.3 JVM Argument Injection via Per-Call Options (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33231 and fix it if it is affected.

What it is: CVE-2026-33231 is a high-severity missing authorization vulnerability in nltk, published on 20 Mar 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-2026-33231 exists.

Affected packages and fixed versions:
- nltk (PyPI): affected all versions; fixed in 3.9.4
- nltk (PyPI): affected all versions; fixed in 3.9.4
- nltk (PyPI): affected all versions; fixed in 3.9.4

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-2026-33231/ (Markdown: https://insights.sbomify.com/CVE-2026-33231/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33231
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33231
- OSV: https://osv.dev/vulnerability/CVE-2026-33231

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33231/
Summaries are generated and may contain mistakes; the official description above is the record.