Sony will be pushing an OTA update to the older Xperia Z, ZR, ZL and Tablet Z models for Android Lollipop (v5.1.1), with the Xperia Z2 and Z3 having already received it. The update, however, reportedly does not fix the Stagefright bug.
The Sony Xperia Z, ZR, ZL, and the Tablet Z models were released in 2013. A few months back, Android v5.0.2 update (build number 10.6.A.0.454) was released for these devices. Newer models such as the Xperia Z2 and Xperia Z3 have already received the v5.1.1 Lollipop update in July. Sony has now started rolling out the v5.1.1 update with build number 10.7.A.0.222, to the older devices. The update will be available for Xperia Z, Xperia ZL, Xperia ZR, and both WiFi and LTE versions of Tablet Z. According to Xperia Blog, these updates are currently being sent out to certain variants of the devices. They include C6602 and C6603 variants of Xperia Z, C6503 and C6506 variants of Xperia ZL, the C5503 version of Xperia ZR, SGP311 and SGP312 models of Tablet Z WiFi, and the SGP321 variant for Tablet Z LTE.
The update apparently fails to completely patch the Stagefright vulnerability that was recently discovered. It exploits a jScript, that leads Android to process video files. Hence, attackers can exploit it by sending a video MMS to a device, even without the user seeing it. Google Hangouts had also been mentioned as a possible avenue of attack. Although Android's versions 4.0 onwards does offer some degree of protection, it is yet to be fully patched. Sony had earlier said that it will release a patch to fix the vulnerability, like other OEMs have already done. It is possible, therefore, that another small update is pushed through after these devices receive the present one.
A few Xperia devices were speculated to directly receive the Android Marshmallow (v6.0) update, although there has been no official word from Sony as yet.