CVE-2026-59880: Immutable: Hash-collision algorithmic complexity denial of service in Immutable.Map/Set

Immutable.Map and Immutable.Set keep keys that share the same 32-bit hash in a collision bucket that is scanned linearly. The string hash is public and deterministic, so an attacker who controls the keys inserted into a Map can craft many keys that all collide, degrading insertion and lookup from amortized O(1) to O(n) per operation — and O(n²) to build or read the whole set. A small, attacker-shaped payload can therefore consume disproportionate CPU and, on a single-threaded runtime such as Node.js, stall the event loop and deny service.