The flash-based vSphere Web Client (6.0 prior to 6.0 U3c and 5.5 prior to 5.5 U3f) i.e. not the new HTML5-based vSphere Client, contains SSRF and CRLF injection issues due to improper neutralization of URLs. An attacker may exploit these issues by sending a POST request with modified headers towards internal services leading to information disclosure.
https://www.vmware.com/security/advisories/VMSA-2017-0017.html