Vulnerability · Published Aug 15, 2026 · Assigned by openjs
CVE-2026-18500@fastify/jwt vulnerable to authorization bypass via global secret overriding the per-request key
High 8.1
In plain English
A high-severity security flaw in @fastify/jwt from @fastify/jwt. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities).
Official description
@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 (as reported)
| Vendor | Product | Versions |
|---|---|---|
| @fastify/jwt | @fastify/jwt | 0 – before 10.2.2 |
Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N