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.
Cookie.php in Piwik before 1.1 does not set the secure flag for the session cookie in an https session, which makes it easier for remote attackers to capture this cookie by intercepting its transmission within an http session.
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.