GHSA-4pcg-wr6c-h9cq
HIGHfastify/websocket vulnerable to uncaught exception via crash on malformed packet
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.
Blast Radius
@fastify/websocket📦@fastify/websocket📦fastify-websocketReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Any application using @fastify/websocket could crash if a specific, malformed packet is sent.
All versions of fastify-websocket are also impacted. That module is deprecated, so it will not be patched.
Patches
This has been patched in v7.1.1 (fastify v4) and v5.0.1 (fastify v3).
Workarounds
No known workaround is available. However, it should be possible to attach the error handler manually. The recommended path is upgrading to the patched versions.
Credits
marcolanaro for finding and patching this vulnerability
For more information
If you have any questions or comments about this advisory:
- Open an issue in @fastify/websocket
- Email us at [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @fastify/websocket | ≥ 5.0.0&&< 5.0.1 | 5.0.1 |
| 📦npm | @fastify/websocket | ≥ 6.0.0&&< 7.1.1 | 7.1.1 |
| 📦npm | fastify-websocket | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @fastify/websocket. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @fastify/websocket to 5.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4pcg-wr6c-h9cq 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 pinpoints whether GHSA-4pcg-wr6c-h9cq is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-4pcg-wr6c-h9cq. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-4pcg-wr6c-h9cq in your dependencies?
O3 detects GHSA-4pcg-wr6c-h9cq across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.