Rack is a modular Ruby web server interface. Prior to versions 2.2.20, 3.1.18, and 3.2.3, Rack::Request#POST reads the entire request body into memory for Content-Type: application/x-www-form-urlencoded, calling rack.input.read(nil) without enforcing a length or cap. Large request bodies can therefore be buffered completely into process memory before parsing, leading to denial of service (DoS) through memory exhaustion.

Users should upgrade to Rack version 2.2.20, 3.1.18, or 3.2.3, anu of which enforces form parameter limits using query_parser.bytesize_limit, preventing unbounded reads of application/x-www-form-urlencoded bodies. Additionally, enforce strict maximum body size at the proxy or web server layer (e.g., Nginx client_max_body_size, Apache LimitRequestBody).