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

• npm @auth/core: < 0.41.3 → fixed in 0.41.3 • npm next-auth: >= 5.0.0-beta.1, < 5.0.0-beta.32 → fixed in 5.0.0-beta.32 • npm next-auth: < 4.24.15 → fixed in 4.24.15

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` `= 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 cannot upgrade immediately: • Enable PKCE (`checks: ["pkce"]`, in addition to `state`/`nonce`) on every provider that supports it; PKCE blocks the practical code-swap variant because the attacker cannot observe the relying party's verifier. • Avoid offering logged-in account linking across multiple providers where one provider is lower-trust or attacker-observable. • Treat `events.linkAccount` as sensitive: add audit logging, user notification, or out-of-band confirmation so that any unexpected link is visible (defense-in-depth, not a root-cause fix). Credit Reported by @Nadav0077. Thank you for the responsible disclosure.