CVE-2026-54270: protobufjs: Memory amplification from preserved unknown fields in binary decode

protobufjs 8.2.0 added support for preserving unknown fields encountered during binary decode. Affected versions preserved unknown wire elements in message.$unknowns and did not provide a decode-time option to discard unknown fields before retaining them.

A crafted protobuf payload containing many unknown fields could therefore cause a decoded message to retain substantially more memory than the input size would suggest, even when unknown-field round-tripping is not needed. protobufjs 8.5.0 added the relevant decode-time options, allowing applications that decode untrusted protobuf data to disable unknown-field retention during decode. protobufjs 8.6.2 flips the default so unknown fields are discarded unless explicitly opted into.