Anyone doing any basic level of seo is using mod_rewrite to make thier urls pretty.
Today the Apache Foundation released versions to fix the exploit within mod_rewrite.
Upgrade your servers and urge your providers to do so asap.
You can read the official announcement here
Depending on the manner in which Apache HTTP Server was compiled, this software defect may result in a vulnerability which, in combination with certain types of Rewrite rules in the web server configuration files, could be triggered remotely. For vulnerable builds, the nature of the vulnerability can be denial of service (crashing of web server processes) or potentially allow arbitrary code execution. This issue has been rated as having important security impact by the Apache HTTP Server Security Team.
This flaw does not affect a default installation of Apache HTTP Server. Users who do not use, or have not enabled, the Rewrite module mod_rewrite are not affected by this issue. This issue only affects installations using a Rewrite rule with the following characteristics:
* The RewriteRule allows the attacker to control the initial part of the rewritten URL (for example if the substitution URL starts with $1)
* The RewriteRule flags do NOT include any of the following flags: Forbidden (F), Gone (G), or NoEscape (NE).
Please note that ability to exploit this issue is dependent on the stack layout for a particular compiled version of mod_rewrite. If the compiler used to compile Apache HTTP Server has added padding to the stack immediately after the buffer being overwritten, it will not be possible to exploit this issue, and Apache HTTP Server will continue operating normally.
The Apache HTTP Server project recommends that all users who have built Apache from source apply the patch or upgrade to the latest level and rebuild. Providers of Apache-based web servers in pre-compiled form will be able to determine if this vulnerability applies to their builds. That determination has no bearing on any other builds of Apache HTTP Server, and Apache HTTP Server users are urged to exercise caution and apply patches or upgrade unless they have specific instructions from the provider of their web server. Statements from vendors can be obtained from the US-CERT vulnerability note for this issue at: