You can check CPU microcode revision on running ESXi host this easy way. Open SSH session to host and then open vsish
[root@esxi:~] vsish -e cat /hardware/cpu/cpuList/0 | grep -i -E 'family|model|stepping|microcode|revision'
Sample output:
Family:6 Model:158 Stepping:11 Number of microcode updates:1 Original Revision:0x0000008e Current Revision:0x000000b4
Source:https://blogs.vmware.com/vsphere/2015/05/using-esxi-6-0-cpu-microcode-loading-feature.html, https://www.thomas-krenn.com/de/wiki/Intel_Microcode_unter_VMware_aktualisieren