Sony Mobile has released a new firmware update in the form of build number 23.4.A.1.236 that is rolling for the Xperia Z2 and Z3 series. This compares to the current version of 23.4.A.1.232. We cannot confirm right now whether the update fully patches the Stagefright exploit (in particular CVE-2015-6602).
The update is only live for the Vodafone network in select European countries. It has been released for the Xperia Z3 (D6603), Xperia Z3 Compact (D5803), Xperia Z2 (D6503) and Xperia Z2 Tablet (SGP521). If you have downloaded the update, let us know your thoughts below.
Update: Looks like the Stagefright exploit remains.
Thanks 3tman and System!