Next.js: Unbounded postponed resume buffering can lead to DoS

Summary

Next.js is a React framework for building full-stack web applications. Starting in version 16.0.1 and prior to version 16.1.7, a request containing the `next-resume: 1` header (corresponding with a PPR resume request) would buffer request bodies without consistently enforcing `maxPostponedStateSize` in certain setups. The previous mitigation protected minimal-mode deployments, but equivalent non-minimal deployments remained vulnerable to the same unbounded postponed resume-body buffering behavior. In applications using the App Router with Partial Prerendering capability enabled (via `experimental.ppr` or `cacheComponents`), an attacker could send oversized `next-resume` POST payloads that were buffered without consistent size enforcement in non-minimal deployments, causing excessive memory usage and potential denial of service. This is fixed in version 16.1.7 by enforcing size limits across all postponed-body buffering paths and erroring when limits are exceeded. If upgrading is not immediately possible, block requests containing the `next-resume` header, as this is never valid to be sent from an untrusted client.