The Galaxy S8, S8+ and Note 8 are receiving One UI/Android Pie beta build but for those who're still on Android Oreo, Samsung is now rolling out a new update for these devices with the latest security improvements.
This update brings the January 2019 security patch that provides fixes to 4 latest Samsung Vulnerabilities and Exposures (SVE) items. It also includes - device performance, features and stability improvements along with bug fixes.
The Galaxy S8 receiving this security patch as build version G955FXXS4CRLB, S8+ as G955FXXS4CRLB and Note 8 as N950FXXS5CSA1 in Spain and also expanding to other countries.
If you want to check this update manually, head into Settings > System updates > Check for system updates or you can simply wait till the update automatically appears on your phone.