How severe is CVE-2021-22964?

CVE-2021-22964 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-22964?

CVE-2021-22964 affects the following packages: fastify-static (npm). Ecosystems affected: npm.

How do I fix CVE-2021-22964?

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.

How do I detect CVE-2021-22964 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify-static, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-22964 if there is no patch (or I can't update yet)?

Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.

Is CVE-2021-22964 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-22964, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-22964?

CVE-2021-22964 has an EPSS (Exploit Prediction Scoring System) score of 1.0%, placing it in the 62th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-22964?

CVE-2021-22964 is classified as Uncontrolled Resource Consumption (CWE-400), Open Redirect (CWE-601). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-22964 published, and has it been updated?

CVE-2021-22964 was published on October 14, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

CVE-2021-22964 — fastify-static

HIGHFix: fastify/fastify-static@c31f17d

CVE-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. A fix is available for fastify-static — see the affected versions and patch details below.

DOS and Open Redirect with user input

Also known asGHSA-pgh6-m65r-2rhq

Published

Oct 14, 2021

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs62th percentile — riskier than 62% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-22964 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.

fastify-staticnpm

102Kdownloads / week

Description

Impact

A redirect vulnerability in the fastify-static module 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.

Patches

The issue has been patched in [email protected]

Workarounds

If updating is not an option, you can sanitize the input URLs using the rewriteUrl server option.

References

Bug founder: drstrnegth
hackerone Report

For more information

If you have any questions or comments about this advisory:

Open an issue in fastify-static
Contact the security team

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`fastify-static`	≥ 4.2.4&&< 4.4.1	4.4.1`npm install fastify-static@4.4.1`

Affected Products

1 product · 1 configurations

Application

fastify-staticfastify

≥ 4.2.4 && < 4.4.1

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

A redirect vulnerability in the `fastify-static` module version >= 4.2.4…

hackerone.comNVDOct 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastify-static, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.

Frequently Asked Questions

### Impact A redirect vulnerability in the `fastify-static` module 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`. ### Patches The issue has been patched in `[email protected]` ### Workarounds If updating is not an