Denial of Service by ReDOS in h2oai/h2o-3

A vulnerability in the `/3/Parse` endpoint of h2oai/h2o-3 version 3.46.0.1 allows for a denial of service (DoS) attack. The endpoint uses a user-specified string to construct a regular expression, which is then applied to another user-specified string. By sending multiple simultaneous requests, an attacker can exhaust all available threads, leading to a complete denial of service.