your answer is on the first google result here (atleast for me, from superuser.com):
http://superuser.com/questions/787576/why-do-i-keep-getting-redirected-to-cgi-bin-redirect-ha-when-using-att-u-ve
basically your modem sucks.
[copy-paste]
"This is a known bug in the Motorola NVG510 modem supplied by AT&T U-Verse."
[/copy-paste]
I would hound your ISP first (att or otherwise), and tier-1 tech support won't be of use to you, get tier-2 on the line asap, if they don't know, ask for tier-3. You will probably have to make multiple calls. After no success there (likely), hound Motorola and ask for tier-2,etc. I see many calls in your future. A field tech isn't likely to help you either, so sending someone out to your house is a waste of time (and they might bill you for it so watch out)
your modem might have settings to tweak to fix it though, or just buy your own modem that doesn't have annoying bugs if you can.