VMware released vCenter Server 6.5 Update 1b (Build 6816762) to fix security issues in Photon OS and few other bugs.
You can already download the update from my.vmware.com site.
Issues resolved in vCenter Server 6.5 Update 1b
Multiple issues are resolved for Photon OS. Apache Struts is updated to version 2.5.13 and Ruby is updated to version 2.4.0-5. Complete list of security issues patched is listed here.
In some cases, a full clone or a cold migration between VMware vSphere on-premises and VMware Cloud on AWS could timeout.
A vCenter Server Appliance configured with vCenter HA might fail after an upgrade to 6.5 Update 1. Root cause for the failure is the renaming of the appliance hostname being changed to the default localhost.localdomain.
vCenter Server Content Library service might fail to start after an upgrade due to a firstboot failure.
For complete details, check the release notes.