# CVE-2026-6270

> Vulnerability · severity: **CRITICAL** (CVSS 9.1).

## Description

@fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers authentication middleware in a parent scope and then registers child plugins with @fastify/middie, the child scope does not inherit the parent middleware. This allows unauthenticated requests to reach routes defined in child plugin scopes, bypassing authentication and authorization checks. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds.

## Key facts

- **CVE ID:** CVE-2026-6270
- **Published:** 2026-04-16
- **CVSS severity:** CRITICAL
- **CVSS base score:** 9.1
- **CWE codes:** CWE-436

## Affected products

- `fastify:fastify\/middie`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6270

## Citation

> AI Analytics. CVE-2026-6270. Retrieved 2026-08-08 from https://api.ai-analytics.org/cve/CVE-2026-6270. Derived from NIST NVD. Licensed CC0.

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