W3 Total Cache Plugin Vulnerability Identified

WordPress news websites have been abuzz this week about an identified vulnerability with the W3 Total Cache WordPress Plugin that leaves databases open for exposure. WordPress security analyst Jason A. Donenfeld published a post on the Full Disclosure List on December 24th outlining the issues revolving around the popular plugin, which is used by several high traffic websites including Lockergnome and Mashable.

With nearly 1.4 million downloads and a Star Rating of 4.6 out of 5 Stars, W3 Total Cache is self-billed as a tool that “improves the user experience of your site by improving your server performance, caching every aspect of your site, reducing the download times and providing transparent content delivery network (CDN) integration.”

W3 Total Cache Plugin Logo

Donenfeld’s Full Disclosure Post

However, the post by Donenfeld gives a detailed run-down of security issues, stating that “Unfortunately, it’s frequently incorrectly deployed. When I set it up by going to the WordPress panel and choosing “add plugin” and selecting the plugin from the WordPress Plugin Catalog (or whatever),
it left two avenues of attack open:

1) Directory listings were enabled on the cache directory, which means anyone could easily recursively download all the database cache keys, and extract ones containing sensitive information, such as password hashes. A simple google search of “inurl:wp-content/plugins/w3tc/dbcache” and maybe some other magic reveals this wasn’t just an issue for me. As W3 Total Cache already futzes with the .htaccess file, I see no reason for it not to add “Options -Indexes” to it upon installation. I haven’t read any W3 documentation, so it’s possible this is a known and documented misconfiguration, but maybe not.

2) Even with directory listings off, cache files are by default publicly downloadable, and the key values / file names of the database cache items are easily predictable. Again, it seems odd that “deny from all” isn’t added to the .htaccess file.”

Shell Script

The security expert added a Shell Script to his entry on December 24th that can both identify and exploit the weakness within the W3 Total Cache plugin. The tool that is designed to speed up websites that use the WordPress Content Management System can make your cache files publicly downloadable even when the Directory Listings are turned off, according to Donenfeld, who also provided a justification for going public with his information.

If I had to categorize these holes, I’d say they’re due to ‘misconfiguration,’ but I figure it’s relevant to write in to full-disclosure & webappsec because I’m usually not horrible with configuring things and I made these mistakes several times without realizing. I’m copying the author on this email, as he may want to include a warning message where nieve folks like myself can see it, or document these somewhere if they’re not already, or at least apply the two .htaccess tweaks mentioned above,” Donenfeld wrote.

News Coverage

In spite of the holiday season and well-deserved vacation days being taken by many important individuals in the WordPress community, the news coverage on the W3 Total Cache vulnerability has been heavy. Stories have been published on TechSpot.com, eSecurityPlanet.com, TheRegister.co.uk, and ghacks.net; among others.

The company that is responsible for the W3 Total Cache Plugin is W3 Edge, which has promised to quickly release an update to the software that will plug the vulnerabilities. However, WordPress blog users who incorporate the plugin may want to disable it until a proven fix has been supplied and tested to the public market.

According to Donenfeld, all a potential hacker would need in the meantime to exploit a website using the W3 Total Cache plugin is to know is the key values and file names of the cache items. We will continue to keep our readers updated on this security issue as events develop.

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W3 Total Cache Plugin Vulnerability Identified

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