A vulnerability has been reported in Mac OS X, allowing malicious web sites to compromise a vulnerable system.

The problem is that code silently delivered using variants of the "disk" URI handler vulnerability described in SA11622, can be executed without using the "help" URI handler.

Two methods have been discussed, allowing malicious websites to execute code from mounted disk images:

1) A disk image or a volume (e.g. AFS, SMB, FTP, or DAV) can register arbitrary URI handlers, which will execute code placed on the disk image when accessing the URI.

2) A disk image or a volume can change an unused URI handler (e.g. TN3270) to execute code placed on the disk image when accessing the URI.

This problem is escalated due to the fact that it by default is possible to silently download and mount disk images using two known methods (silent download and execution of "safe" files and the "disk" URI). Furthermore, it is reportedly also possible to mount volumes using other methods such as SMB, AFS, FTP, DAV and others.

This vulnerability has been confirmed on a fully patched Mac OS X systems (including the patch "Security Update 2004-05-24 for Mac OS X" released by Apple, which fixes the "help" URI handler vulnerability) running versions 10.3.3 and 10.3.4.

Reportedly, working exploits using "ftp" exist, but also "afp" seems to be a likely attack vector.
It may also be possible to use "ssh" to open a connection to a remote site allowing the remote site to gain direct access to a vulnerable system.

The core of the problem seems to be the design of URI handling in Mac OS X. It is likely that many other URI handlers are affected in various ways.

Attack vectors include browsers and programs supporting Mac OS X URI handling.

Solution
Apple has issued Security Update 2004-06-07, which addresses the vulnerability by presenting users with a dialog box the first time a file is launched automatically.
Further details available to Secunia VIM customers

Provided and/or discovered by
Information about this was first provided to Secunia by Jens Jakob Jensen from ozwix.dk.

Changelog
Further details available to Secunia VIM customers

Original Advisory
Apple Security Updates:
http://www.apple.com/support/security/security_updates.html

About Security Update 2004-06-07:
http://docs.info.apple.com/article.html?artnum=25785

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers