The VMM must implement replay-resistant authentication mechanisms for network access to privileged accounts.

A replay attack may enable an unauthorized user to gain access to the VMM. Authentication sessions between the authenticator and the VMM validating the user credentials must not be vulnerable to a replay attack. An authentication process resists replay attacks if it is impractical to achieve a successful authentication by recording and replaying a previous authentication message. A privileged account is any VMM account with authorizations of a privileged user. Techniques used to address this include protocols using nonces (e.g., numbers generated for a specific one-time use) or challenges (e.g., TLS, WS_Security). Additional techniques include time-synchronous or challenge-response one-time authenticators.