Thanks but this is from AA not UA. Can I still stay secure side?
No. According to this:
http://www.flysfo.com/web/page/non-flash/airlines/
Cathay Pacific flies from the A gates. The United-International connector provides airside access to the
G gates. You will be required to re-clear security.
That said, this connection should be a breeze assuming bags are interlined and there is no significant delay by AA.