[tor-relays] Performance issues/DoS from outgoing Exit connections

Hello,

on the evening of 2022-10-18, we (Artikel10) started getting alerts about our Tor servers, while our traffic declined sharply. When we investigated, we found that there were hundreds of thousands of TCP connections (per server) open to a single address, orders of magnitude more than any other address. We blocked this address via "ExitPolicy reject", then another one, and since then things seem to have improved.

I have thrown together a small Python script to detect this and generate "ExitPolicy reject" lines automatically: https://github.com/artikel10/surgeprotector

This is still experimental, so if you decide to give the script a try, please keep an eye on it.

Kind regards, Alexander