Piwik before 1.11 accepts input from a POST request instead of a GET request in unspecified circumstances, which might allow attackers to obtain sensitive information by leveraging the logging of parameters.
Piwik 1.1 allows remote attackers to obtain sensitive information via a direct request to a .php file, which reveals the installation path in an error message, as demonstrated by plugins/Widgetize/Widgetize.php and certain other files.