js-yaml: Quadratic-complexity (O(n^2)) DoS via !!omap tag in YAML11_SCHEMA

Summary js-yaml v5.x introduces YAML11SCHEMA support with the !!omap ordered map tag. The omapTag.addItem function performs a linear On scan for duplicate key detection on every insertion, resulting in On^2 total time to parse a document with n omap entries. An attacker can send a small crafted...