Advisories for Composer/Symfony/Yaml package

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 input can blow up into a multi-gigabyte structure and exhaust memory: the classic "Billion Laughs" denial-of-service against any parser exposed to untrusted YAML.

Symfony\Component\Yaml\Parser::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.]+.\n#u', whose [\d.]+ and . overlap on the dot, that exhibit catastrophic backtracking on crafted input. A single oversized %YAML directive header (or comment / document-marker line) makes the parser hang for an arbitrarily long time, denying service.

Symfony\Component\Yaml\Parser is the entry point for parsing YAML strings into PHP values via Yaml::parse(). When the parser is exposed to attacker-controlled input, deeply nested mappings or sequences cause both the block-level (Parser::parseBlock()) and inline (Inline::parseSequence() / Inline::parseMapping()) parsers to recurse without a depth limit. A crafted document exhausts the PHP stack and crashes the worker.

Symfony 2.0.x before 2.0.22, 2.1.x before 2.1.7, and 2.2.x remote attackers to execute arbitrary PHP code via a serialized PHP object to the (1) Yaml::parse or (2) Yaml\Parser::parse function, a different vulnerability than CVE-2013-1348.

The Yaml::parse function in Symfony remote attackers to execute arbitrary PHP code via a PHP file.