wpForo 1.2 comes with new options to control New Registered users. I recommend to read the changelog when you update and you’ll know all changes. There is an option to not allow new users post a link and this option is manageable. Just navigate to Forums > Tools > Antispam admin page and change the "Min number of posts user must have to post a link" option value. You can set it 0 if you don’t want to limit them.