Next.js 15.1+ Broken Outside Vercel: SEO Nightmare & Security Flaw

Next.js 15.1 and later versions are severely broken outside of Vercel deployments. Vercel's metadata streaming, intended for performance optimization, breaks metadata handling on non-Vercel platforms, crippling SEO. Search engine crawlers can't read the JavaScript-generated metadata, and even static builds require JavaScript execution for metadata. Furthermore, version 15.1.8 contains a critical security vulnerability (CVE-2025-29927), patched only in 15.2.3. This article strongly advises against using Next.js 15.1+ and suggests considering alternatives to avoid Vercel lock-in and potential security risks.