plugins/system/highlight/highlight.php in Joomla! 3.0.x through 3.0.2 and 2.5.x through 2.5.8 allows attackers to unserialize arbitrary PHP objects to obtain sensitive information, delete arbitrary directories, conduct SQL injection attacks, and possibly have other impacts via the highlight parameter.  Note: it was originally reported that this issue only allowed attackers to obtain sensitive information, but later analysis demonstrated that other attacks exist.