The Custom Button Installer dialog in Google Toolbar 4 and 5 beta presents certain domain names in the (1) "Downloaded from" and (2) "Privacy considerations" sections without verifying domain names, which makes it easier for remote attackers to spoof domain names and trick users into installing malicious button XML files, as demonstrated by presenting www.google.com when the button was downloaded from an arbitrary site through an open redirector on www.google.com.

Cross-site scripting (XSS) vulnerability in Google Toolbar 2.0.114.1 allows remote attackers to inject arbitrary web script via about.html in the About section. NOTE: some followup posts suggest that the demonstration code's use of the res:// protocol does not cross privilege boundaries, since it is not allowed in the Internet Zone. Thus this might not be a vulnerability.

The Google toolbar 1.1.58 and earlier allows remote web sites to monitor a user's input into the toolbar via an "onkeydown" event handler.