After a thorough analysis, it was discovered that a perpetrator compromised a network by gaining...

The best way to mitigate the issue of a perpetrator compromising a network by gaining access to the network through an SSL VPN gateway by guessing a username and brute forcing the password is to use two-factor authentication mechanisms. Two-factor authentication is a method of verifying the identity of a user or device by requiring two different types of factors, such as something the user knows (e.g., password, PIN, etc.), something the user has (e.g., token, smart card, etc.), or something the user is (e.g., biometric, fingerprint, etc.). Two-factor authentication can enhance the security of the network access by making it harder for attackers to impersonate or compromise the legitimate users or devices. If the perpetrator only knows the username and password, they will not be able to access the network without the second factor, such as a token or a biometric34 References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 6: Communication and Network Security, p. 321; Official (ISC)2 CISSP CBK Reference, Fifth Edition, Domain 4: Communication and Network Security, p. 449.