Bogus user/pass authentication prompt on nxdomains

[watchpocket]

When I want to log into my router's web interface, I enter the following into my browser's address bar and hit return:

http://192.168.1.1/Status_Router.asp

(Actually, I have that bookmarked.)

My browser (Firefox 26.0) then immediately displays a dialog box with the following text:

A username and password are being requested by http://192.168.1.1. The site says: "BuffaloStreet-dd-wrt"

("BuffaloStreet-dd-wrt" is what I've named my router.)

Just below that text in the dialog box are two fields prompting for User Name and Password.

Fine, no problem. This is known as the browser's HTTP Basic Authentication prompt.


The problem comes when I enter into my browser's address bar an nxdomain (non-existent domain), or any name that doesn't resolve: The exact same dialog box pops up.

This time the message is almost, but not quite, identical:

A username and password are being requested by http://name-that-doesn't-resolve. The site says: "BuffaloStreet-dd-wrt"

In all cases, entering User/Pass takes me to the router's web interface. But this dialog box should not be appearing at all when names entered in the address bar don't resolve.

Same thing happens when I run Firefox in safe mode.

This leads me to believe that I've misconfigured something in my router settings, but what?

I'm using Ubuntu 12.04 with Gnome Classic. The router is a Buffalo WZR-HP-AG300H, with firmware version: DD-WRT v24-sp2 (04/13/11) std - build 16785.

My question is: What's causing this to happen? Thanks.