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...

PT-2026-44150

Description SymfonyComponentYamlParser::cleanup strips the optional %YAML directive header, leading comments, and document start/end markers before parsing. The original regexes contained overlapping quantifiers, most notably '^%YAML: d.+. u', whose d.+ and . overlap on the dot, that exhibit...

Uncontrolled Recursion

Overview Affected versions of this package are vulnerable to Uncontrolled Recursion via Unbounded Recursion in Nested Blocks, Sequences, and Mappings. Symfony\Component\Yaml\Parser is the entry point for parsing YAML strings into PHP values via Yaml::parse. When the parser is exposed to...