This attack could pose a serious security threat. You should take immediate action to stop any damage or prevent further damage from happening.
This signature will detect attempts to exploit a Buffer Overflow Vulnerability in Apple iTunes.
Apple iTunes is a media player for Microsoft Windows and Apple MAC OS X.
The application is prone to a stack-based buffer-overflow vulnerability because it fails to perform adequate boundary checks before copying user-supplied data to an insufficiently sized buffer. This issue can occur when iTunes parses specially crafted 'itms', 'itmss', 'daap', 'pcast', and 'itpc' URIs.
Attackers can leverage this issue to execute arbitrary code with the privileges of the user running the affected application. Failed attacks will likely cause denial-of-service conditions.
The vendor has released an advisory and fixes. Please see the references for details.