CVE-2026-107391: music-metadata: MP4 stsd sample-entry size==0 causes a synchronous infinite loop (DoS) — unreleased regression on master

StsdAtom.get() in lib/mp4/AtomToken.ts parses an MP4 stsd (sample description) box’s entry table by advancing a cursor with off += size - 4, where size is a 32-bit, attacker-controlled per-entry length read straight from the file. When size == 0, that advance is 0, so a file declaring a huge entry_count and a first entry size of 0 spins forever: same bytes read every iteration, no progress, no exit. Because StsdAtom.get runs synchronously inside strtok3’s tokenizer, this doesn’t just fail slowly — it blocks the Node.js event loop entirely for the whole process. A 48-byte file is enough to hang any service that parses user-uploaded audio/video metadata through parseBuffer, parseFile, parseStream, parseBlob, or parseWebStream.

This is currently unreleased — present on the master branch only, not in the latest npm release (11.14.0) or any earlier one. Reporting now, before it ships.