A vulnerability has been reported in Mac OS X, allowing malicious web sites to compromise a vulnerable system, Secunia reports. Secunia collects, validates, and verifies all vulnerability reports issued by security research groups, vendors, and others.
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 system (including the patch “Security Update 2004-05-24 for Mac OS X” released by Apple, which fixes the “help” URI handler vulnerability).
Reportedly, working exploits using “ftp” exists, also “afp” seems to be a likely vector.
Attack vectors include browsers and programs supporting Mac OS X URI handling.
Apple has not yet released patches for these issues.
The following two steps prevent malicious web sites from placing code on a vulnerable system, using the two known methods (silent download and execution of “safe” files and the “disk” URI). However, it does not prevent execution of code from already mounted images:
1) Uncheck (“Open “safe” files after downloading”).
2) Add a protocol helper (application) for “disk” and “disks”.
To prevent other methods of mounting volumes, it is necessary to change the protocol helper for all unnecessary protocols (URI handlers), this should include at least “ftp” and “afp”, but also “cifs”, “file” “ftps”, “nfs”, “smb” and “ssh” are recommended.
More info here.
Related MacDailyNews article:
Unsanity updates free utility to fix latest Mac OS X ‘URL Schemes’ vulnerability – May 24, 2004