When receiving an HTTP request from a client, the Relay plugin keeps all the header lines received until the end of headers is found.
There is no limit for the allocated buffer, and this happens before the client is authenticated.
A malicious unauthenticated client sending an unlimited number of header lines can lead to memory exhaustion and the WeeChat process can be killed by the OOM killer.
Mitigation
Unload relay plugin with command: /plugin unload relay and see: /help weechat.plugin.autoload.