GHSA-4QPC-3HR4-R2P4 Symfony's YAML Parser Vulnerable to Exponential Memory Allocation via Recursive Collection-Alias Expansion ("Billion Laughs")

Description Symfony\Component\Yaml\Parser resolves YAML aliases anchor during parsing. Aliases that reference collections arrays, stdClass, TaggedValue-wrapped collections can themselves point to other collections containing aliases, creating exponential expansion at resolution time. A small inpu...