Pyloris is a slow HTTP DoS tool which enables the attacker to craft its own HTTP request headers. These include the packet header, cookies, packet size, timeout and CRLF option.
Pyloris objective is to keep TCP connections open for as long as possible between the attacker and the victims servers. This results in exhausting the server's connection table resources. Once the connection table of the server is exhausted, it will not be able to handle new connections from legitimate users, resulting in a denial-of-service.