Google today uploaded the updated factory images for its roster of Nexus devices with the April security patch. The company is yet to start the rollout of the OTA update, but with the factory images available, the OTA update should not be far behind.
While the March security patch update for the Nexus 6P and Nexus 5X also brought about some performance improvements, the April security patch update is squarely aimed at fixing exploits or other security issues in Android.
The security bulletin from Google indicates that 29 security bugs were found and fixed by Google and other independent researchers in this update. The most critical security issues were related to remote code execution vulnerabilities discovered in mediaserver, media codec and libstagefright processes of the OS. More details about these exploits and their severity can be found here.
If you cannot wait for the OTA update, which should land on your Nexus device within a week from now, you can always flash the factory image by downloading it from here.