Contents of .svn directories, when located under an Apache web root, are viewable via a browser. This leads to potential exploits, as referenced by Adam Gotterer.

The hack obviously starts in .svn directory, specifically at the entries file. You can access this file by browsing to:
http://www.somedomain.com/.svn/entries?

This document contains all of the files and folders svn manages in that directory. In some instances you can locate admin directories and the same thing applies…
http://www.somedomain.com/admin/.svn/entries?

So at this point all you have are a bunch of file names. Sometimes you can get some fun information and access to files that were meant to be hidden. Security by obscurity is not a solution, protect files you don’t want the public to access!

Now this is where things get interesting… Any file that has been checked in I can now execute. Either directly or through an svn folder that holds file revisions. Pick any file in the list and browse to:
http://www.somedomain.com/.svn/text-base/filename.php.svn-base

... and so on.