Checking today BDL-SFO you would have misconnected as the plane was late arriving at BDL.
That said, it is scheduled to arrive at Gate 75 which is about as close to Int'l as you can ask for, and no, you do not have to reclear security.

The last two times (this month) I flew to SFO, I had to wait over 30 min in a holding area for a gate. This would pretty much mean a missed connection. I wouldn't risk this at all.

Use the Interactive Maps feature for Terminal 3 and International G here for an overview of the layout of SFO: https://www.flysfo.com/maps/

And here's UA's own SFO terminal map: https://www.united.com/web/en-us/con...fo.aspx?POS=US