Safari Errorjacking Vulnerability and Exploit [Patched]

One of the vulnerabilities patched in Safari 5.0.4 is a fairly critical issue in WebKit (CVE-2011-0167) that allows Javascript to jump into the local zone, and access any file on the local computer that is accessible to the current user. This could be used by malicious websites to extract files and information from the victim’s computer. The vulnerability affects Safari on Mac OS X and Windows, and could affect other WebKit-based browsers, although Chrome is safe due to added restrictions.

The bug exists because most browser error pages are loaded from the local “file:” zone, a zone that Javascript is not normally allowed to access directly. Since a child browser window remains under the control of the parent, it is possible to cause a child browser window to error, thus entering the normally-restricted local zone, and then instructing the child window to access local files using this elevated local-zone privilege.

This issue was a nice catch, discovered by Aaron Sigel who has a detailed explanation, video demo and proof-of-concept on his blog. It probably goes without saying, but Safari users should run Software Update as soon as possible.