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🛡️ CVE-2026-6414 — fastify-static

🟡 CVSS 5.9 — Medium ✅ No Known Exploit CWE-177 NVD
5.9
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity none, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: None.
  • Availability impact: None.

Weakness class

CVE-2026-6414 is classified as CWE-177: Improper Handling of URL Encoding (Hex Encoding). The product does not properly handle when all or part of an input has been URL encoded.

Affected software

CVE-2026-6414 is recorded against 2 packages.

  • @fastify/static
  • fastify-static (from 8.0.0 up to 9.1.1)

Timeline and source

Published on 16 April 2026 and last revised on 8 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
github.com (Web)
github.com (Web)
nvd.nist.gov (Advisory)
cna.openjsf.org (Web)
github.com (Package)

Other advisories for this package

@fastify/static has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-177: Improper Handling of URL Encoding (Hex Encoding)) in other software:

Details

Severity Medium
CVSS Score 5.9
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
CWE CWE-177
Public Exploit ✅ No
Source NVD
Published 2026-04-16
Updated 2026-08-20
Modified 2026-07-08
Fix URL N/A

Affected Packages

Software From version Fixed in
@fastify/static — —
fastify-static 8.0.0 9.1.1

Similar Threats

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