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.
https://exchange.xforce.ibmcloud.com/vulnerabilities/64641
http://www.securityfocus.com/bid/45787