Drupal 6.x before 6.31 and 7.x before 7.27 does not properly isolate the cached data of different anonymous users, which allows remote anonymous users to obtain sensitive interim form input information in opportunistic situations via unspecified vectors.
https://drupal.org/SA-CORE-2014-002
http://www.openwall.com/lists/oss-security/2014/04/22/2