@fastify/oauth2 vulnerable to Login CSRF via OAuth state cookie not cleared after callback

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

@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.

Source published

19 Oct 2026 13:24:27 UTC

Source modified

19 Oct 2026 14:26:45 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 4.2 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N