Unbounded Recursion in Symfony's YAML Inline Lexer: Understanding and Defending Against CVE-2026-109413
CVE-2026-109413 is a high-severity vulnerability in Symfony's YAML parser that allows an attacker to crash the process with a single, specially crafted YAML document. This vulnerability affects any code parsing untrusted YAML, particularly when using `#[MapRequestPayload]` with the Yaml component. Understanding the root cause and attack vector is crucial for defenders to implement effective mitigations.