GHSA-x445-f3h2-j279: Auth.js: OAuth state, nonce, and PKCE check cookies are not bound to the provider that created them

Summary Auth.js stores the OAuth/OIDC anti-CSRF checks (state, nonce, and the PKCE verifier) in global cookies that are not bound to the provider that created them. On callback, a check value minted during a sign-in started with one provider can satisfy the callback for a different provider, because the stored cookie is not verified against the callback provider's identity (provider id, issuer, client id, or redirect URI). In a multi-provider app that allows account linking while logged in, this provider-confusion / mix-up condition can let an attacker link their account at a second provider to a victim's user. Am I affected? You may be affected if all of the following hold: - You use next-auth <= 4.24.14 or >= 5.0.0-beta.1, <= 5.0.0-beta.31, or @auth/core <= 0.41.2. - You configure multiple OAuth/OIDC providers. - You allow users to link additional providers while logged in. - At least one configured provider's authorization request is observable by an attacker, and at least one target provider's callback can be satisfied without a PKCE verifier (i.e. it relies only on state or only on nonce). You are not affected if you use a single OAuth provider, do not allow logged-in account linking, or all providers enforce PKCE. Impact - Account-linking confusion: an attacker can get their account at a target provider linked to the victim's Auth.js user, granting the attacker persistent sign-in to the victim's account through that linked provider. - Exploitation requires luring the victim into starting a legitimate same-origin flow; it cannot be performed by cross-site request forgery alone, which reduces practical likelihood. Patched version The fix binds the OAuth check cookies to the provider/authorization flow that created them, so a callback cannot consume a check value minted for a different provider. Upgrade to the first releases containing this fix (pending; this advisory will be updated with exact patched versions before publication). Workarounds If you c