Starman versions before 0.4019 for Perl allow a stalled request body to hold a worker indefinitely, as read_timeout covers only the headers.
Content-Length and chunked request bodies are read with blocking reads and no deadline. A client that sends complete headers and then stalls or trickles the body keeps the worker waiting until it disconnects.
A remote attacker can take every worker with a few such connections, five with the default worker count, so the server stops answering requests.
Version 0.4019 applies read_timeout to each wait for body data and adds a body_timeout limit, 300 seconds by default, on the total time to read a body.
Upgrade to Starman 0.4019 or later.