AFAIK QUIC traffic is impossible to attack using MITM techniques. So I wonder how the GFW handles it. Do they block it entirely or still filter it somehow?
It's not hard to identify those channels and block them. A connection used to interact with websites has completely different traffic patterns compared to a user sending all of their traffic over one specific connection.
Add to that the fact that large video streaming services such as YouTube, where you may see large quantities of data being exchanged over persistent connections, are already blocked in China, and your VPN becomes quite obvious without seeing even a byte of plaintext.
Of course for common protocols like QUIC they have their own custom solution (linked in a sibling comment), but the point is that even with encrypted SNI you will need dedicated anti-GFW protocols to stand a chance against censorship. No protocol that works well for most consumers is going to protect against the analysis a dedicated firewall with decent funding can come up with.
AFAIK, the only thing that stops an MITM attack (where they respond as if they’re the remote server and then relay to the real remote server) are certificates.
If an authority requires you trust their root certificate so they can spy on you, QUIC will not make any difference.
You might think IP checks are safe because everything's on Cloudflare and they can't block Cloudflare, but you'd be wrong. Even Spain blocks Cloudflare (yes, entirely) during football games.
Anyways, my point wasn't that a government can't MITM using a root cert. My point is that the government can't do so secretly. The whole world will know if they try.
https://en.wikipedia.org/wiki/File:HTTP-1.1_vs._HTTP-2_vs._H...
Here is good intro for you:
The Security Challenges of HTTP/3 and QUIC — What You Need to Know https://medium.com/@RocketMeUpCybersecurity/the-security-cha...