You can download the patch for your version here: http://members.vbulletin.com/patches.php
To install the patch:
1) Download the appropriate files for your version of vBulletin 5
2) Upload all files found within the zip file. Make sure to overwrite the existing files on your server.
If you are using a version of vBulletin 5 Connect prior to 5.2.1, you are encouraged to upgrade as soon as possible to protect your content.
vBulletin Cloud sites have already had this fix applied.
5.2.2 Patch Level 1
5.2.1 Patch Level 1
5.2.0 Patch Level 3
This issue has been resolved in 5.2.3 Release Candidate 3. Customers using a pre-release copy of 5.2.3 are encouraged to upgrade as soon as possible.