Vulnerability Note VU#999708

Apple Safari automatically executes arbitrary shell commands or code

Apple Safari is a web browser that comes with the Mac OS X operating system.

Explicit binding

Mac OS X supports a feature called explicit binding, which LaunchServices examines to determine which application is used to open a file. If explicit binding is specified for a file, this setting will override the application association for the file type. Explicit binding information is stored in the resource fork for a file.

"Safe" files

By default, Safari will automatically open "safe" file types, such as pictures, movies, and archive files, including ZIP files. If the contents of an archive file are also considered safe, then Safari will automatically open the contents after the archive is extracted.

The problem

A data file with explicit binding can allow an attacker to execute arbitrary commands or code on systems running Safari. Limited testing shows that Safari apparently fails to check for the presence of explicit binding data when determining if a file is "safe" or not.

II. Impact

Proof of concept code is publicly available.

III. Solution

Install Apple Security Update 2006-001 and Apple Security Update 2006-002, which provide updates to Safari, LaunchServices, and CoreTypes. These updates improve the method that Safari uses to determine if a file is safe.

Disable "Open 'safe' files after downloading"

Disable the option "Open 'safe' files after downloading," as specified in the Securing Your Web Browser document. This will help prevent automatic exploitation of this and other vulnerabilities.

Systems Affected

http://docs.info.apple.com/article.html?artnum=303382
http://docs.info.apple.com/article.html?artnum=303453
http://www.mathematik.uni-ulm.de/numerik/staff/lehn/macosx.html
http://www.heise.de/english/newsticker/news/69862
http://developer.apple.com/documentation/Carbon/Conceptual/LaunchServicesConcepts/LSCConcepts/chapter_2_section_8.html
http://developer.apple.com/technotes/tn/tn2017.html
http://developer.apple.com/documentation/mac/MoreToolbox/MoreToolbox-11.html
http://docs.info.apple.com/article.html?artnum=108009
http://secunia.com/advisories/18963/
http://www.securityfocus.com/bid/16736
http://xforce.iss.net/xforce/xfdb/24808
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0397
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0398
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0399
http://securitytracker.com/alerts/2006/Feb/1015652.html

Credit

This vulnerability was publicly disclosed by Michael Lehn.

This document was written by Will Dormann.

Other Information

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