The Portal for ArcGIS Security 2018 Update 2 Patch has been released for Portal for ArcGIS 10.3.1.
ArcGIS Enterprise Administrators should consider installing this patch as high priority, as it addresses an incorrect proxy access control vulnerability, among others.
Security patches are released for the last minor release in a series of ArcGIS products that are still in mainstream support.
All versions of this patch are available here:
Portal for ArcGIS Security 2018 Update 2 Patch
Users can also run the ArcGIS Patch Notification tool to check for, download, and install patches.
Check for and install software patches and updates—ArcGIS Server (Windows) Installation Guide (10.5)...
