secuvera-SA-2014-01: Reflected XSS in W3 Total Cache

Affected Products
    W3 Total Cache 0.9.4 (older releases have not been tested)

    "The only WordPress Performance Optimization (WPO) framework; 
    designed to improve user experience and page speed. (..)
    W3 Total Cache improves the user experience of your site by 
    increasing server performance, reducing the download times 
    and providing transparent content delivery network (CDN) 
    integration."

References
    https://wordpress.org/plugins/w3-total-cache/
    https://www.secuvera.de/advisories/secuvera-SA-2014-01.txt
    https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-8724

Summary:
    If the option "Page cache debug info" is enabled, W3 Total 
    Cache adds some HTML-Comments including the "Cache key" which 
    is the URL itself. The URL is just reflected without any output 
    encoding.

Effect:
    An attacker could include clientside Scriptcode in a request, 
    which will be reflected by the application. Using some social 
    engineering an attacker would be able to compromise users of 
    the application.

Vulnerable Scripts:
    Debug Function

Examples:
    https://$victim/nothing--<script>alert("XSS")</script>

Solution:
    Install bug fix release. Always make sure to disable debug function 
    in productive environments.

Disclosure Timeline:
    2014/09/17 vendor contacted via https://www.w3-edge.com/contact/
    2014/10/07 vendor reacted including a first patch preview
    2014/10/14 notified vendor the patch does not address the issue
    2014/10/24 vendor sent a second patch preview 
    2014/12/10 vendor published 0.9.4.1 release
    2014/12/16 public disclosure

Credits:
    Tobias Glemser, secuvera GmbH
    tglemser@secuvera.de
    https://www.secuvera.de

Disclaimer:
    All information is provided without warranty. The intent is to 
    provide information to secure infrastructure and/or systems, not
    to be able to attack or damage. Therefore secuvera shall 
    not be liable for any direct or indirect damages that might be 
    caused by using this information.