NextAuth.js vulnerabilities

NextAuth.js from 5.0.0-beta.0 until 5.0.0-beta.32 has a vulnerability where applications that gate access by checking only for the existence of the auth object can fail open when Auth.js has a server configuration error. A non-OK session response is parsed into a truthy error object instead of null, so checks such as !!auth evaluate to true for unauthenticated requests.

NextAuth.js prior to @auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32 has a vulnerability in the email normalizer, where an address with a fullwidth at-sign (U+FF20) passes validation but after Unicode normalization becomes a standard @, potentially causing the sign-in link to be delivered to an attacker.

NextAuth.js before @auth/core 0.41.3, next-auth 4.24.15, and 5.0.0-beta.32 stores OAuth/OIDC anti-CSRF state, nonce, and PKCE verifier in global cookies not bound to the provider. An attacker can exploit this to link their account to a victim's account in multi-provider apps with account linking.

NextAuth.js before @auth/core 0.41.3, next-auth 4.24.15, and 5.0.0-beta.32 can throw an uncaught exception in getToken() when reading a malformed Authorization: Bearer header. When no session cookie is present, getToken() URL-decodes the bearer value before validation, and malformed percent encoding causes decodeURIComponent() to throw. This can lead to per-request denial of service without exposing tokens or bypassing authentication.