The ESXi Host Client in VMware ESXi (6.5 before ESXi650-201712103-SG, 5.5 before ESXi600-201711103-SG and 5.5 before ESXi550-201709102-SG) contains a vulnerability that may allow for stored cross-site scripting (XSS). An attacker can exploit this vulnerability by injecting Javascript, which might get executed when other users access the Host Client.
https://www.vmware.com/security/advisories/VMSA-2017-0021.html