On March 20, Mozilla Corporation released new security and stability updates for both versions of its Firefox browser and for its Internet application suite, SeaMonkey. The new updates eliminate a situation where a malicious web page hosted on a specially-coded FTP server could exploit a minor FTP PASV port-scanning vulnerability to perform a rudimentary port-scan of machines inside the victims firewall. 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, a spokesperson said. 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, but Mozilla clients will now ignore the alternate server address.
News source: DesktopLinux