4.2.3 is a maintenance release that fixes issues identified in 4.2.2.
Please note if you use https in the AdminCP, but not on the front-end, the auto-upgrade process may not work correctly. You should download this update from the client area and upgrade manually.
This release addresses an XSS vulnerability and we recommend all clients upgrade as soon as possible. We would like to thank @newbie LAC for responsibly disclosing the details of this vulnerability to us.