Cross-site scripting (XSS) vulnerability in the W3 Total Cache plugin before 0.9.4.1 for WordPress, when debug mode is enabled, allows remote attackers to inject arbitrary web script or HTML via the "Cache key" in the HTML-Comments, as demonstrated by the PATH_INFO to the default URI.
https://wordpress.org/plugins/w3-total-cache/changelog/
http://www.securityfocus.com/archive/1/534266/100/0/threaded