that is bad... but typical for the arrogance of AppleYou can't.
All versions of iOS are unable to upload files from the Safari browser. That is not XenForo exclusive - Safari does not allow you to upload files from any website.
This changes in iOS 6 where I believe Apple have updated Safari to support this.
EDIT: In the interim, Tapatalk allows you to upload files from its app, but that's an add-on you would need to install on your forum and an app your users would need to purchase.
Considering the most recent rumoured release date for the next iPhone is September 12, I'd say they will release it just before that date or on the day. That rumoured date could change.Does anybody know,when the new ios6 will be available for the normal human beeings?