Symfonyに脆弱性（CVE-2026-109413）

### Description `Yaml\Parser::lexInlineStructure()` recursed through `lexInlineMapping()` and `lexInlineSequence()` for every `{` and `[` of an inline collection, without entering the nesting level that the rest of the parser bounds with `maxNestingLevel`. A document made of deeply nested inline collections, such as `[[[[...]]]]`, exhausted the stack while it was being lexed: depending on the PHP version and its stack settings, the process crashed or the request ended with a fatal error. Any code parsing untrusted YAML is affected. That includes `#[MapRequestPayload]` when the Yaml component is installed and the endpoint does not restrict `acceptFormat`: a single unauthenticated request with a YAML content type is enough. ### Resolution The inline lexer now enters and leaves the same nesting level as the rest of the parser, so nested inline collections are bounded by `maxNestingLevel`, and the parser raises a `ParseException` beyond it. The patches for this issue are available [here](https://github.com/symfony/symfony/commit/2a8bf9c58d862b0c76a35ce288d1ba6a27223aad) for branch 5.4 (and forward-ported to 6.4, 7.4, 8.1 and 8.2). ### Credits We would like to thank Nicolas Grekas for reporting the issue and providing the fix. ### References - Fix: [#65688](https://github.com/symfony/symfony/pull/65688)