Monoceros versions before 0.30 for Perl allow a request declaring a large Content-Length to kill a worker by exhausting memory.
The request body is read in a loop that asks sysread for all of the remaining declared length at once. Perl grows the read buffer to that size before any data arrives, so a length larger than available memory makes the worker exit with an uncatchable out of memory error before the application is called.
A remote attacker can force a worker restart with each request of a few bytes.
Upgrade to Monoceros 0.30 or later.