Apple released an updated version of iOS 12 on Wednesday

almost one year after the last update, to patch a security vulnerability that was recently fixed in newer versions of the OS 

The time and effort to update your iPhone 5S, 6 or 6 Plus is worth it - Apple rarely releases security updates for older software 

so users know it's a fairly significant problem when it happens.

If visitors open an infected website in Safari or perhaps another browser

The vulnerability fixed by iOS 12.5.6 could allow it to run unrestrained software on your phone. 

Furthermore, Apple claims that someone else in the world may have attempted to use this exploit

That's not an alarming situation - it's fairly common, but you should probably remain cautious until you notify the company