The auth0/nextjs-auth0 SDK validates that the returnTo parameter is a same-origin URL. The SDK then stores this value and, in a later step, reconstructs it for the post-authentication redirect. The reconstruction logic can produce a URL that browsers interpret as an absolute or scheme-relative path, leading to a redirect to an unintended domain.

Description In affected versions of the Next.js SDK, simultaneous requests that trigger a nonce retry may cause the proxy cache fetcher to perform improper lookups for the token request results.

Which Projects are Affected? Users are affected if they meet all of the following preconditions: - Applications using the auth0/nextjs-auth0 SDK, versions 4.12.0 to 4.17.0, and - Applications using the proxy handler /me/ and /my-org/ with DPoP enabled.

Affected product and versions Auth0/nextjs-auth0 v4.12.0 to 4.17.0

Resolution Upgrade Auth0/nextjs-auth0 version to v4.18.0 or greater

Acknowledgements Okta would like to thank Reynaldo Immanuel for their discovery and responsible disclosure.