Executive brief
Auth0's Next.js SDK is used by developers to integrate authentication into Next.js applications. Under specific conditions involving simultaneous authentication requests with cache enabled, the SDK may improperly serve cached authentication tokens to unintended users, potentially exposing user identity information and allowing unauthorized access to user resources.
Technical details
The vulnerability is a race condition (improper cache lookup) in the proxy cache handler of Auth0's Next.js SDK versions 4.12.0–4.17.0. When simultaneous requests trigger nonce retry logic with DPoP (Demonstrating Proof-of-Possession) enabled on the /me/* and /my-org/* proxy endpoints, the cache fetcher fails to properly isolate token lookup results, causing one user's cached authentication token to be served to another concurrent request. This requires the attacker to have low-level privileges and user interaction to trigger, but can expose confidential user data. The vulnerability is patched in version 4.18.0.
Affected products
- Auth0 Next.js SDK 4.12.0 to 4.17.0
Timeline
- 2026-04-21: disclosed: GHSA-xq8m-7c5p-c2r6 published
- 2026-04-21: patched: Fixed in version 4.18.0