Couchbase 4.5 introduces a new security feature called SCRAM-SHA, aimed at enhancing user authentication and defending against brute-force attacks. This mechanism, which stands for Salted Challenge Response Authentication Mechanism, improves upon the previous CRAM-MD5 login scheme by exchanging hashed items between the client and server, which cannot be replayed. SCRAM is adaptable, supporting various hash algorithms like SHA1, SHA-256, and SHA-512, with Couchbase defaulting to the highest level of security, SHA-512. To utilize SCRAM-SHA, users need to upgrade to Couchbase 4.5, and the SDK will manage the authentication process, reverting to CRAM-MD5 for older Couchbase versions if necessary. While SCRAM-SHA offers enhanced security features, using TLS is still recommended for optimal protection.