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.
The Parser now tracks recursion depth in a shared ParserState object across both block-level and inline parsing, with a default limit of 128. The limit is configurable via a new $maxNestingLevel argument on Parser::__construct(), Yaml::parse() and Yaml::parseFile().
The patch for this issue is available here for branch 5.4.
Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.
| Software | From | Fixed in |
|---|---|---|
symfony / yaml
|
- | 5.4.52 |
symfony / symfony
|
- | 5.4.52 |
symfony / symfony
|
6.0.0 | 6.4.40 |
symfony / symfony
|
7.0.0 | 7.4.12 |
symfony / symfony
|
8.0.0 | 8.0.12 |
symfony / yaml
|
6.0.0 | 6.4.40 |
symfony / yaml
|
7.0.0 | 7.4.12 |
symfony / yaml
|
8.0.0 | 8.0.12 |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
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