CVE-2026-109413: Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process
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.
References
- github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-109413.yaml
- github.com/FriendsOfPHP/security-advisories/blob/master/symfony/yaml/CVE-2026-109413.yaml
- github.com/advisories/GHSA-2v3c-qxhr-7vpv
- github.com/symfony/symfony/commit/116287c3b5bc057e7a0420d2e52d384e14ea9417
- github.com/symfony/symfony/commit/2a8bf9c58d862b0c76a35ce288d1ba6a27223aad
- github.com/symfony/symfony/commit/8fb436fed9658a79d220e9f2b1ba8a2095559018
- github.com/symfony/symfony/commit/ab61e6cfd35042f16840a00f485eab2481dd4c2a
- github.com/symfony/symfony/pull/65688
- github.com/symfony/symfony/releases/tag/v5.4.54
- github.com/symfony/symfony/releases/tag/v6.4.45
- github.com/symfony/symfony/releases/tag/v7.4.18
- github.com/symfony/symfony/releases/tag/v8.1.6
- github.com/symfony/symfony/security/advisories/GHSA-2v3c-qxhr-7vpv
- nvd.nist.gov/vuln/detail/CVE-2026-109413
- symfony.com/blog/cve-2026-109413-unbounded-recursion-in-the-yaml-inline-lexer-lets-a-single-document-crash-the-process
- symfony.com/cve-2026-109413
Code Behaviors & Features
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