The vCenter Server contains a denial-of-service vulnerability due to improper XML entity parsing. A malicious actor with non-administrative user access to the vCenter Server vSphere Client (HTML5) or vCenter Server vSphere Web Client (FLEX/Flash) may exploit this issue to create a denial-of-service condition on the vCenter Server host.
https://www.vmware.com/security/advisories/VMSA-2021-0020.html