What’s Vulnerable › Vulnerabilities

CVE-2026-6414: @fastify/static vulnerable to route guard bypass via encoded path separators

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-16 · updated 2026-06-17
• Weakness: CWE-177

Description

@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that protect files served by @fastify/static. For example, a route guard on a protected path can be circumvented by encoding the path separator in the URL. Upgrade to @fastify/static 9.1.1 to fix this issue. There are no workarounds.

Affected products

• https://github.com/fastify/fastify-static: from 8.0.0 before 9.1.1 — fixed in 9.1.1

How to fix

Upgrade to a fixed version: https://github.com/fastify/fastify-static 9.1.1. Check the vendor advisory for mitigations.

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/fastify-static/security/advisories/GHSA-x428-ghpx-8j92
• https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69p
• https://github.com/honojs/hono/security/advisories/GHSA-q5qw-h33p-qvwr

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