With a recent HAProxy update on our reverse proxy VM I decided to enable http/2, disable TLS 1.0 and drop support for non forward-secrecy ciphers.

Tested our sites in Chrome and Firefox, all was well, went to bed.

Next morning a medium-critical havock went loose. Our ERP system couldn't create tickets in our ticket system anymore, the ticket systems Outlook AddIn refused to connect, the mobile app we use to access our anti-spam appliance wouldn't connect although our internal blackboard app still connected over the same load balancer without any issues.

So i declared a 10min maintenance window and disabled HTTP/2, thinking that this was the culprit.

Nope. No dice.
Okay, i thought, enable TLS 1.0 again.

Suddenly the ticket system related stuff starts to work again.

So since both the ERP system and the AddIn run on .NET i dug through the .NET documentation and found out that for some fucking reason even in the newest .NET framework version (4.7.2) you have to explicitly enable TLS 1.1 and 1.2 or else you just get a 'socket reset' error. Why the fuck?!

Okay, now that i had the ticket system out of the way i enabled HTTP/2 and verified that everything still works.

It did, nice.

The anti-spam appliance app still did not work however, so i enabled one non-pfs cipher in the OpenSSL config and tested the app.

Behold, it worked.

I'm currently creating a ticket with them asking politely why the fuck their app has pfs-ciphers disabled.

And I thought disabling DEPRECEATED tech wouldn't be an issue... Wrong...