UAA defaults email address to an insecure domain

Cloud Foundry UAA, versions prior to 73.0.0, falls back to appending “unknown.org” to a user's email address when one is not provided and the user name does not contain an @ character. This domain is held by a private company, which leads to attack vectors including password recovery emails sent to a potentially fraudulent address. This would allow the attacker to gain complete control of the user's account.