I'm a freshman in university, and I recently moved into residence. Pretty quickly, I logged into campus wifi so I can actually do classes and things.
My laptop and primary phone logged in with minimal complaining, but my secondary/legacy phone had problems. I went to the site that explained how to log into the wifi, but one step told me to choose as my CA certificate "Use system certificates". No such option was available. I wound up having to go to yet another university website, and download a certificate they provided, but it still refused to connect. I never even saw the "Domain" textbox open like it wanted me to.
Today, I revisited the issue. I checked wifi connection instructions for other OSs, and one (Chromebook) said to leave it as "Do not check/None installed". I tried it out, telling it to not use a certificate, and, lo and behold, it connected. I checked the network settings, and it had spontaneously added the university certificate I'd gotten off of the website. Now I'm a little worried there was or now is some kind of vulnerability.
TL;DR: Joined a network with CA Certificate set to "Don't validate" out of desperation. It connected, and set itself to a safety certificate I had downloaded, and now seems to work fine. Is there anything to be worried about?