CVE-2026-110008: @fastify/oauth2 vulnerable to Login CSRF via OAuth state cookie not cleared after callback

Severity: medium (CVSS 4.2 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-19 · updated 2026-10-19
Weakness: CWE-352

Description

@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.

Affected products

@fastify/oauth2: from 7.2.0 before 8.3.2 — fixed in 8.3.2

How to fix

Upgrade to a fixed version: @fastify/oauth2 8.3.2. Check the vendor advisory for mitigations.

References

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