Where does Asterisk "ignore malformed messages"

Hi,
I’m trying to understand Asterisk’s source code better. I know that certain malformed messages, such as messages, where the cseq counter is too high, just get fully ignored and don’t even send a 404 error to the client. Where in the code/ in what file does it do this?

Kind regards!

Asterisk doesn’t. The PJSIP stack does, before it even gets to any code in Asterisk itself.