The image module in Drupal 7.x before 7.14 does not properly check permissions when caching derivative image styles of private images, which allows remote attackers to read private image styles.
http://www.securityfocus.com/bid/53359
http://www.mandriva.com/security/advisories?name=MDVSA-2013:074
http://secunia.com/advisories/49012
http://drupalcode.org/project/drupal.git/commit/3bf6761ff7537dc68e22ea73f155134f3cfd41a8
http://drupal.org/node/1557938