GHSA-xmf8-cvqr-rfgj: 
JavaScript vulnerability analysis and mitigation

Summary

The exported getToken() helper (next-auth/jwt and @auth/core/jwt) can throw an uncaught exception when it reads a malformed Authorization: Bearer … header. When no session cookie is present, getToken() URL-decodes the bearer value before validating it, and malformed percent-encoding causes the decode step to throw rather than being treated as an invalid token. Because getToken() is commonly called in API routes, middleware, and other request handlers, a single unauthenticated request can trigger an unhandled exception in code paths that authenticate requests.

Am I affected?

You are affected if all of the following hold:

• You use next-auth <= 5.0.0-beta.25 (or @auth/core exposing the same getToken() implementation).
• Your application calls getToken() directly — for example in a Route Handler, middleware, or server-side request handler.
• You do not wrap that getToken() call in your own try/catch. You are not affected if you only use the framework's auth() helper and never call getToken() yourself, or if every getToken() call site already has its own exception handling.

Impact

• Denial of service: an unauthenticated request carrying a malformed Bearer authorization header can raise an unhandled exception in any handler that calls getToken().
• The impact is per-request and limited to availability; it does not expose tokens, sessions, or other data, and does not bypass authentication. CWE-20: Improper Input Validation.

Patched version

The fix makes getToken() treat a malformed Bearer value as an invalid token and return null, matching how other undecodable tokens are already handled. Upgrade to the first release containing this fix (to be published; this advisory will be updated with the exact patched version before publication) and no code changes are required.

Workarounds

If you cannot upgrade immediately, either:

• Config/code-level: wrap your getToken() calls so a thrown error is treated as "no token", e.g.

  let token = null
  try {
    token = await getToken({ req, secret })
  } catch {
    token = null
  }

• Or strip/normalize the incoming Authorization header at the edge (proxy, middleware) before it reaches getToken(), rejecting values whose Bearer portion is not valid percent-encoding.

Credit

Reported by @deprrous. Thank you for the responsible disclosure.