Inefficient Algorithmic Complexity

Summary

shell-quote prior to 1.8.5 finalizes parsed tokens in `parse()` using `Array.prototype.concat` as a reduce accumulator, which reallocates and copies the entire growing array on every iteration. As a result `parse()` runs in O(n^2) time relative to the number of input tokens. An attacker who can supply an attacker-controlled string to any code path that calls `parse()` (no shell metacharacters are required; plain space-separated words suffice) can block the single-threaded Node.js event loop for an extended period with a small input, resulting in a denial of service. There is no code execution or data disclosure; impact is to availability only. Fixed in 1.8.5.