CVE-2026-6414: Fastify Fastify-Static

Medium severity, CVSS 5.9. EPSS: 0.4% chance of exploitation in the next 30 days.

@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

• Fastify Fastify-Static: from 8.0.0, before 9.1.1 (fixed in 9.1.1)

Published 2026-04-16. Last modified 2026-06-17.