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Re: Wordpress Remote Exploit - W3 Total Cache
From: Frederick Townes <ftownes () w3-edge com>
Date: Fri, 28 Dec 2012 11:42:53 -0600

For those of you that use W3 Total Cache to make your sites more performant, thank you. Security issues are always of 
paramount interest, no matter the scope.
 
The root of the possible vulnerability lies in the intersection of two configuration settings, one at the Web Server 
level and the other at the W3 Total Cache database caching level. You may be vulnerable if the following are true: your 
server is configured to allow directory listing with enabled public access on W3TC’s database caching directories and 
also use database caching via the disk caching method. These settings would allow a hacker to break the md5 hashing 
used for the then publicly accessible cached database objects. The manner, extent and timing of the vulnerability’s 
report leave much to be desired; nonetheless, the versions have now been patched on wordpress.org. Thanks to those that 
offered remediation advice. I’m sorry for the delay in turning this around, none of the proposed solutions were 
satisfactory.
 
The hotfix (tested with WordPress version 3.5) will help those who are just now upgrading to 0.9.2.4 or are otherwise 
getting started with W3 Total Cache. Specifically, the hash logic is improved via wp_hash(), significantly stronger 
than the previous md5 hashing at the compromise of a bit of speed. I’ve also made sure that a web server’s lack of 
security around directory listings and the standard file structure of W3TC’s hashing logic are no longer of consequence 
for those attempting to download them from your server.
 
For those who are using database caching to disk already, please be sure to disable directory indexing and deny web 
access to the “wp-content/w3tc/dbcache/” directory in your web configuration, then empty the database cache for good 
measure. Or, simply deactivate W3 Total Cache, uninstall it, and re-install it via wordpress.org to have the hotfix 
applied upon re-activation. Again, empty the database cache for good measure. Your settings will not be lost during 
this process. If all of this is gibberish to you, then simply disable database caching to disk until the next release 
or use another method if available. Once again, empty the database cache using the button of the same name available on 
the database caching settings tab.
 
If you’re reading this and have seen a post about the issue that does not have this response on it, please do post this 
for me. Thanks in advance. Happy Holidays.
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