The scenario described involves an attacker conducting an aggressive ARP scan followed by multiple SSH Server Banner and Key Exchange Initiations. The lack of visibility into the encrypted data transmitted over the SSH channel suggests that the attacker may have gained access by brute-forcing the SSH service. This method involves attempting numerous combinations of usernames and passwords until the correct credentials are found, allowing unauthorized access to the server.
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Understanding Cisco Cybersecurity Operations Fundamentals (CBROPS) course1.
Cisco Cybersecurity documents and resources