Next.js is a React framework for building full-stack web applications. From 16.0.0 until 16.3.8, the `next dev` development server exposes a Model Context Protocol endpoint without reliably restricting cross-site requests. A malicious website visited by a developer can reach the endpoint and read the project's disk location, source code snippets from error reports, route inventory, and development logs. Production deployments do not serve this endpoint. This issue is fixed in version 16.3.8.