CVE-2021-22964
HIGHCVE-2021-22964 is a high-severity (CVSS 8.8) Uncontrolled Resource Consumption vulnerability in fastify-static. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether CVE-2021-22964 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
DOS and Open Redirect with user input
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
fastify-staticnpmDescription
A redirect vulnerability in the fastify-static module version >= 4.2.4 and < 4.4.1 allows remote attackers to redirect Mozilla Firefox users to arbitrary websites via a double slash // followed by a domain: http://localhost:3000//a//youtube.com/%2e%2e%2f%2e%2e.A DOS vulnerability is possible if the URL contains invalid characters curl --path-as-is "http://localhost:3000//^/.."The issue shows up on all the fastify-static applications that set redirect: true option. By default, it is false.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | fastify-static | ≥ 4.2.4&&< 4.4.1 | 4.4.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify-static. 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-static to 4.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-22964 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 CVE-2021-22964 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 CVE-2021-22964. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-22964 in your dependencies?
O3 detects CVE-2021-22964 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.