How severe is CVE-2026-6414?

CVE-2026-6414 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-6414?

CVE-2026-6414 affects the following packages: @fastify/static (npm). Ecosystems affected: npm.

How do I fix CVE-2026-6414?

Update @fastify/static to 9.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6414 is resolved across your whole dependency graph.

How do I detect CVE-2026-6414 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-2026-6414 if there is no patch (or I can't update yet)?

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.

Is CVE-2026-6414 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-6414 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-6414?

CVE-2026-6414 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 37th 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-2026-6414?

CVE-2026-6414 is classified as CWE-177 (CWE-177). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-6414 published, and has it been updated?

CVE-2026-6414 was published on April 16, 2026 and was last updated on October 28, 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

MEDIUM severity

CVE-2026-6414 — @fastify/static

MEDIUM

CVE-2026-6414 is a medium-severity (CVSS 5.9) CWE-177 vulnerability in @fastify/static. A fix is available for @fastify/static — see the affected versions and patch details below.

@fastify/static vulnerable to route guard bypass via encoded path separators

Also known asGHSA-x428-ghpx-8j92

Published

Apr 16, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-6414.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs37th percentile — riskier than 37% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

2Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@fastify/staticnpm

8.5Mdownloads / week

Description

Impact

@fastify/static v9.1.0 and earlier decodes percent-encoded path separators (%2F) before filesystem resolution, but Fastify's router treats them as literal characters. This creates a routing mismatch: route guards on /admin/* do not match /admin%2Fsecret.html, but @fastify/static decodes it to /admin/secret.html and serves the file.

Applications that rely on route-based middleware or guards to protect files served by @fastify/static can be bypassed with encoded path separators.

Patches

Upgrade to @fastify/static >= 9.1.1.

Workarounds

None. Upgrade to the patched version.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@fastify/static`	≥ 8.0.0&&< 9.1.1	9.1.1`npm install @fastify/static@9.1.1`

Affected Products

1 product · 1 configurations

Application

fastify-staticfastify

≥ 8.0.0 && < 9.1.1

range

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 9.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6414 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.

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.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-6414 (CC BY 4.0)

Frequently Asked Questions

### Impact `@fastify/static` v9.1.0 and earlier decodes percent-encoded path separators (`%2F`) before filesystem resolution, but Fastify's router treats them as literal characters. This creates a routing mismatch: route guards on `/admin/*` do not match `/admin%2Fsecret.html`, but @fastify/static decodes it to `/admin/secret.html` and serves the file. Applications that rely on route-based middleware or guards to protect files served by @fastify/static can be bypassed with encoded path separators. ### Patches Upgrade to `@fastify/static` >= 9.1.1. ### Workarounds None. Upgrade to the pat