Fastify is a fast, low overhead web framework for Node.js. Applications specifying different validation strategies for different content types may bypass validation by providing a slightly altered content type, such as with different casing or altered whitespace before the semicolon (;). This issue affects applications using a specific schema pattern where individual content types are defined with their own schemas. The initial patch in version 5.3.1 did not fully address the problem, and a complete fix was released in version 5.3.2 and 4.29.1.