A crash happens when decoding a malformed websocket frame in relay plugin.
This happens even if a password is set in relay plugin, the malformed websocket frame can be received before the authentication of the client.
There are multiple ways to mitigate this issue:
Rremove all relays, see: /help relay
Unload relay plugin with command: /plugin unload relay and see: /help weechat.plugin.autoload
Secure relay to allow only some trusted IP addresses, see: /help relay.network.allowed_ips