If you are still using iPhone 5s, iPhone 6, you must download this security update 

Apple in the release note has asked the users of the iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad mini 2, iPad mini 3, and iPod touch (6th generation) to update to iOS 12.5.4.

If you are still using an iPhone 5s, iPhone 6 or iPhone 6 Plus and gadgets running iOS 12, Apple has an important update for you. The latest security update patches three vulnerabilities which affect the memory corruption and WebKit, that may have been exploited. The list of devices includes iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad Mini 2, iPad mini 3, and iPod touch (6th generation). Apple in the release note has asked the users of the iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad mini 2, iPad mini 3, and iPod touch (6th generation) to update to iOS 12.5.4. “This update provides important security updates and is recommended for all users,” Apple says. It is important to note that Apple did not roll out the iOS 13 for iPhone 5s, iPhone 6 and others but Apple continued rolling out updates to fix vulnerabilities found in the WebKit. Apple has revealed that two out of three WebKit vulnerabilities may have been actively exploited. "Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited,” Apple said. So basically, if you have any of the old Apple devices listed above, you should immediately update your device.