The issue is a XSS vulnerability. XSS (Cross Site Scripting) issues allow scripts and malicious HTML to be injected into the page, potentially allowing data theft or unauthenticated access.
Specifically, the issue relates to specially crafted text entered into messages and output using the structured text system (used in profile posts and comments).
There are no other fixes included in this version. There will be a further maintenance release in the coming weeks.
Applying a Fix: Upgrading
You may upgrade to 2.0.11 to fix this issue. You should upgrade as you would to any other release.
Customers with an active license may download 2.0.11 from their customer area. Full details for how to install and upgrade XenForo can be found in the XenForo Manual.
Applying a Fix: Patching
Alternatively, this issue can be fixed by applying the patch in the attached file. You should simply overwrite the following file with the version attached to this message:
Xenforo 2.0.11 released (security fix)