A crash happens when decoding a malformed HTTP message in relay plugin, protocol "api".
This happens even if the client is not authenticated, the HTTP message is parsed before the authentication.
Mitigation
There are multiple ways to mitigate this issue:
Rremove all relays with protocol "api", 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