Mozila released Firefox 2.0.0.3 and Firefox 1.5.0.11 security updates. The update fixeds an FTP-related security hole, described as "FTP PASV port-scanning" by Mozilla. The FTP protocol includes the PASV (passive) command which is used by Firefox to request an alternate data port. The specification of the FTP protocol allows the server response to include an alternate server address as well, although this is rarely used in practice.

A malicious web page hosted on a specially-coded FTP server could use this feature to perform a rudimentary port-scan of machines inside the firewall of the victim. By itself this causes no harm, but information about an internal network may be useful to an attacker should there be other vulnerabilities present on the network.

The updated Firefox browsers will now ignore the alternate server address.

For a list of changes and more information, review the Firefox 1.5.0.11 Release Notes and the Firefox 2.0.0.3 Release Notes.

Firefox 1.5.0.11 and Firefox 2.0.0.3 are available for Windows, Mac, and Linux for free download from http://getfirefox.com.