CVE-2026-18500: Fastify Fastify/jwt

High severity, CVSS 8.1. EPSS: 0.3% chance of exploitation in the next 30 days.

@fastify/jwt is a JSON Web Token plugin for Fastify. In versions before 10.2.2, a per-request verification key passed to request.jwtVerify({ key }) is silently overridden by the plugin's globally configured secret, because the option merge applies the global key last. Applications that use different keys for different authorization domains, for example separate user and admin keys, therefore accept a token signed with the global key on a route that explicitly requires another key. This lets an ordinary authenticated user cross a key-based trust boundary without knowing either secret. The issue is fixed in @fastify/jwt 10.2.2, where an explicit per-call key takes precedence over the global secret. Users should upgrade to 10.2.2.

Affected products

• Fastify Fastify/jwt: before 10.2.2 (fixed in 10.2.2)

Published 2026-08-15. Last modified 2026-09-04.