Samsung Galaxy A5(2017) started to receive February 2018 security patch as an OTA. The update is currently started to rollout in Russia and it might be available soon in other countries as well. It changes the build number for the A5 (2017) firmware is A520FXXU4BRB1.
February security patch fixes five critical vulnerabilities found in Android, along with 16 possible exploits in Samsung’s software February patch also brings fixes for the Meltdown and Spectre vulnerabilities if the device is not already updated to January security patch.
If the update is not popped up head to settings-> software update -> Downloads update manually.