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

Summary

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.

Impact

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.

Patches

Fixed by enforcing size limits across all postponed-body buffering paths and erroring when limits are exceeded.

Workarounds

If upgrade is not immediately possible:

• Block requests containing the next-resume header, as this is never valid to be sent from an untrusted client.