CVE-2026-109413 — Vulnerability intelligence
PHP / Composer — symfony/symfony, symfony/symfony, symfony/symfony, symfony/symfony, symfony/yaml, symfony/yaml, symfony/yaml, symfony/yaml
Original source text (not a translation)
Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process
### 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)