The vBulletin team recently disclosed a XSS (cross site scripting) vulnerability in the uploader.swf file that is included by default on vBulletin 4 and 5. This file comes from the YUI library that is not supported anymore, so the vBulletin team is recommending everyone remove that file asap from their installs.
This is their full note:
It has come to our attention that there is a security issue in the uploader.swf file included as part of the Yahoo User Interface (YUI) library included in vBulletin 4. As the version of YUI included in vBulletin is end-of-lifed, Yahoo will not be fixing this issue.
The vulnerable file is also present in the vBulletin 5 download package though not used by the vBulletin 5 front-end. We recommend that you delete the file and replace it with the attached file.
To resolve this issue take the following steps:
-Delete uploader.swf located in clientscript/yui/uploader/assets or /core/clientscript/yui/uploader/assets
-Replace it with the attached file.
If you run vBulletin, please remove that file as soon as you can. Note that users of our website application firewall are already protected against this threat.