UseBB contains a flaw that allows a remote cross-site scripting (XSS) attack. This flaw exists because the application does not validate the BBCode color value. This may allow a user to create a specially crafted URL that would execute arbitrary script code in a user's browser within the trust relationship between their browser and the server.
Upgrade to version 0.5.1a or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.