CVE-2025-48947 is a high-severity vulnerability affecting the Auth0 Next.js SDK versions 4.0.1 through 4.6.0. This SDK is widely used to implement user authentication in Next.js web applications. The vulnerability arises because the `__session` cookies set by the auth0.middleware component lack appropriate Cache-Control headers. Consequently, when these applications are deployed behind Content Delivery Networks (CDNs) or edge caching systems that cache HTTP responses, the sensitive session cookies can be inadvertently cached and stored by these intermediaries. This caching behavior violates secure handling of authentication tokens, potentially exposing sensitive session information to unauthorized parties who can access the cached content. The vulnerability requires three conditions to be met: the application must use an affected version of the nextjs-auth0 SDK, the application must be deployed behind a CDN or edge cache that caches responses containing Set-Cookie headers, and the Cache-Control headers must be missing or improperly configured on sensitive responses. Exploitation could lead to unauthorized access to user sessions, compromising confidentiality and integrity of user data. The vulnerability has a CVSS 4.0 base score of 7.7, reflecting its high impact and relatively low complexity to exploit, with partial user interaction and no authentication required. The recommended remediation is to upgrade the nextjs-auth0 SDK to version 4.6.1 or later, where this issue is patched by properly setting Cache-Control headers to prevent caching of sensitive cookies. No known exploits are currently reported in the wild, but the widespread use of this SDK and common deployment patterns involving CDNs make this a significant risk.

For European organizations, this vulnerability poses a substantial risk to web applications that rely on the Auth0 Next.js SDK for user authentication, especially those using CDN or edge caching services to improve performance and scalability. If exploited, attackers could retrieve cached session cookies from CDN caches, enabling session hijacking and unauthorized access to user accounts. This can lead to data breaches involving personal data protected under GDPR, resulting in regulatory penalties and reputational damage. The confidentiality and integrity of user sessions are directly threatened, potentially allowing attackers to impersonate users or escalate privileges. Availability impact is limited but could occur if attackers use stolen sessions to perform malicious actions that disrupt services. Given the popularity of Next.js and Auth0 in modern web development, many European startups, SMEs, and large enterprises using these technologies could be affected. The risk is amplified in sectors with high-value data such as finance, healthcare, and e-commerce. Organizations using CDNs without strict cache control policies are particularly vulnerable.

1. Immediate upgrade of the Auth0 Next.js SDK to version 4.6.1 or later, which includes the fix for proper Cache-Control header settings to prevent caching of sensitive cookies. 2. Review and audit CDN and edge caching configurations to ensure that responses containing authentication cookies or other sensitive headers are never cached. This includes explicitly setting Cache-Control headers such as 'no-store, no-cache, private' on all authentication-related responses. 3. Implement security headers like 'Set-Cookie' with 'HttpOnly' and 'Secure' flags to reduce cookie exposure. 4. Conduct penetration testing and security reviews focusing on caching behavior in the deployment environment. 5. Monitor CDN logs and cache hit/miss patterns for anomalies that could indicate unauthorized access attempts. 6. Educate development and DevOps teams about secure caching practices and the risks of caching authentication tokens. 7. If immediate upgrade is not feasible, consider disabling CDN caching for authentication endpoints as a temporary mitigation. 8. Ensure that session management follows best practices, including short session lifetimes and token invalidation on logout.