CVE-2026-110008

1th percentile - higher than 1% of all known CVEs

@fastify/oauth2 is a Fastify wrapper for OAuth2 login flows. In versions 7.2.0 through 8.3.1, the state and code-verifier cookies are set without a Path attribute at a login route with two or more path segments, while the clearing step at the OAuth callback writes them with a root path, so the original cookies survive the callback and the documented single-use guarantee for the state value does not hold. A state value an attacker learns stays valid for the rest of the browser session, letting the attacker drive their own authorization flow in the victim's browser and sign the victim in to the attacker's account (login CSRF). The issue is fixed in @fastify/oauth2 8.3.2, and users should upgrade to 8.3.2 or later. As a workaround, set an explicit cookie path so the set and the clear name the same cookie.

An attacker could log the victim into their account, potentially leading to unauthorized actions on behalf of the victim or data leakage. The risk affects applications using @fastify/oauth2 in vulnerable versions.

Update @fastify/oauth2 to version 8.3.2 or later. If updating is not possible, set an explicit cookie path for state and code-verifier so that setting and clearing target the same cookie.