# How plex is doing HTTPS for all its users

May 25, 2022

https://words.filippo.io/how-plex-is-doing-https-for-all-its-users/

Interesting dive into how Plex is creating certs for every plex server

This way when a server first starts it asks for its wildcard certificate to be issued (which happened almost instantly for me) and then the client, instead of connecting to http://1.2.3.4:32400, connects to https://1-2-3-4.625d406a00ac415b978ddb368c0d1289.plex.direct:32400 which resolves to the same IP, but with a domain name that matches the certificate that the server (and only that server, because of the hash) holds.

found via this tweet

The end of DNS rebinding is nigh! With a bit of luck and some time, maybe it will also mean DNS resolvers can stop breaking public domains that resolve to internal addresses, making https://words.filippo.io/how-plex-is-doing-https-for-all-its-users/ more viable!

P.S.: I finally figured out why they advise you might need to turn off DNS rebinding protections: a domain like 192-168-1-7.###.plex.direct which resolves to a local IP (that they use when you want to connect to a server on your LAN while still using the HTTPS web app) is exactly what a rebinding attack needs to access vulnerable services behind your firewall. See for example this post by Michele Spagnuolo.