Piwik before 1.1 does not properly limit the number of files stored under tmp/sessions/, which might allow remote attackers to cause a denial of service (inode consumption) by establishing many sessions.

Piwik before 1.1 does not prevent the rendering of the login form inside a frame in a third-party HTML document, which makes it easier for remote attackers to conduct clickjacking attacks via a crafted web site.

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.

The Piwik_Common::getIP function in Piwik before 1.1 does not properly determine the client IP address, which allows remote attackers to bypass intended geolocation and logging functionality via (1) use of a private (aka RFC 1918) address behind a proxy server or (2) spoofing of the X-Forwarded-For HTTP header.

Multiple cross-site scripting (XSS) vulnerabilities in Piwik before 1.1 allow remote attackers to inject arbitrary web script or HTML via unspecified vectors.

Cross-site scripting (XSS) vulnerability in the Login form in Piwik 0.1.6 through 0.5.5 allows remote attackers to inject arbitrary web script or HTML via the form_url parameter.

The loadContentFromCookie function in core/Cookie.php in Piwik before 0.5 does not validate strings obtained from cookies before calling the unserialize function, which allows remote attackers to execute arbitrary code or upload arbitrary files via vectors related to the __destruct function in the Piwik_Config class; php://filter URIs; the __destruct functions in Zend Framework, as demonstrated by the Zend_Log destructor; the shutdown functions in Zend Framework, as demonstrated by the Zend_Log_Writer_Mail class; the render function in the Piwik_View class; Smarty templates; and the _eval function in Smarty.

Piwik 0.2.32 and earlier stores sensitive information under the web root with insufficient access control, which allows remote attackers to obtain the API key and other sensitive information via a direct request for misc/cron/archive.sh.