H2O Vulnerable to Denial of Service (DoS) via `/3/ParseSetup` Endpoint

A vulnerability in the /3/ParseSetup endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service (DoS) attack. The endpoint applies a user-specified regular expression to a user-controllable string. This can be exploited by an attacker to cause inefficient regular expression complexity, leading to the exhaustion of server resources and making the server unresponsive.