Critical Severity Vulnerability
This vulnerability has been rated as Critical severity. Immediate action is recommended.
CVE-2026-6270
Critical
Low
Medium
High
Critical
9.1
CVSS Score
Vulnerability 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.
CVSS Metrics
Common Vulnerability Scoring System
Vector String:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack Vector
N
Attack Complexity
L
Privileges Required
N
User Interaction
N
Scope
U
Confidentiality
H
Integrity
H
Availability
N
References & Resources
-
https://cna.openjsf.org/security-advisories.htmlce714d77-add3-4f53-aff5-83d477b104bb Vendor Advisory
-
https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9cce714d77-add3-4f53-aff5-83d477b104bb Exploit Mitigation Vendor Advisory
-
https://github.com/fastify/middie/security/advisories/GHSA-72c6-fx6q-fr5wce714d77-add3-4f53-aff5-83d477b104bb Vendor Advisory
Severity Details
9.1
out of 10.0
Critical
Weakness Type (CWE)
CWE-436
Interpretation Conflict
- Description
- Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
- Typical Severity
- Medium
- Abstraction Level
- Class
Key Information
- Published Date
- April 16, 2026
