Executive brief
The Auth0 Next.js SDK is a library that developers use to add authentication and user management to web applications. When multiple user requests are processed simultaneously by the same SDK instance, the library may incorrectly cache and retrieve token data, potentially allowing one user's authentication tokens to be returned to another user. This could enable an attacker to impersonate other users and access their accounts or sensitive data.
Technical details
The vulnerability is an improper authorization/cache lookup issue (CWE-863) in the TokenRequestCache component of the Auth0 Next.js SDK. When handling concurrent requests with a singleton SDK instance, the cache lookup fails to properly differentiate between simultaneous requests, resulting in cross-request token leakage. The attack requires network access and low-level privileges, but user interaction and specific timing conditions are needed. An attacker can extract authentication tokens belonging to other concurrent users, potentially achieving account takeover or unauthorized access to protected resources. The vulnerability affects versions 4.11.0, 4.11.1, and 4.12.0; patches are available in versions 4.11.2 and 4.12.1.
Affected products
- Auth0 Next.js SDK 4.11.0, 4.11.1, 4.12.0
Timeline
- 2025-12-10: disclosed
- 2025-12-10: patched: Fixed in versions 4.11.2 and 4.12.1