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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.9 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-6414: 0.42% estimated exploitation activity in the next 30 days; percentile 36.55 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

16 Apr 2026, 22:34 UTC

Last modified by the source

8 Jul 2026, 08:14 UTC

Source last checked

26 Oct 2026, 12:48 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-x428-ghpx-8j92

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-x428-ghpx-8j92

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# Patch Next advisory brief: CVE-2026-6414

Advisory: @fastify/static vulnerable to route guard bypass via encoded path separators
IDs: CVE-2026-6414, GHSA-x428-ghpx-8j92
Record: https://patchnext.com/advisories/cve-2026-6414 (revision 2, source checked 26 Oct 2026, 12:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @fastify/static 9.1.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @fastify/static: affected >= 8.0.0, <= 9.1.0; fixed in 9.1.1

## Suggested inspection (read-only)
- `npm ls @fastify/static --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @fastify/static.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-x428-ghpx-8j92 (OSV record GHSA-x428-ghpx-8j92 lists affected ranges: npm @fastify/static >=8.0.0 <9.1.1 (fixed))
- Verified: https://github.com/advisories/GHSA-x428-ghpx-8j92 (GitHub-reviewed advisory GHSA-x428-ghpx-8j92 lists affected ranges: npm @fastify/static >=8.0.0 <=9.1.0)

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