Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, 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. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

Affected: Packagist: symfony/yaml, Packagist: symfony/symfony

### Description

`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.

### Resolution

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](https://github.com/symfony/symfony/commit/914f427ed9630ddb3904dafba763e53d9f133fe3) for branch 5.4.

### Credits

Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.

Affected: Ubuntu:16.04:LTS: symfony, Ubuntu:Pro:18.04:LTS: symfony, Ubuntu:Pro:20.04:LTS: symfony, Ubuntu:Pro:22.04:LTS: symfony, Ubuntu:Pro:24.04:LTS: symfony, Ubuntu:25.10: symfony, Ubuntu:26.04:LTS: symfony

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, 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. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

Ein Angreifer kann mehrere Schwachstellen in Zabbix ausnutzen, um einen Denial of Service Angriff durchzuführen, und um Sicherheitsvorkehrungen zu umgehen.