In a Risk Matrix, risk levels are determined by the intersection of the likelihood of an occurrence (probability) and the consequence of that occurrence (impact). When the probability of an event is very high and the impact is major, it typically falls into the 'Extreme' category. This is because the combination of a high likelihood and major impact represents a scenario where the risk is unacceptable and requires immediate attention and mitigation measures.
References: The EC-Council's Certified SOC Analyst (CSA) course materials and study guides provide detailed information on assessing risks using a Risk Matrix. The course emphasizes the importance of understanding the Risk Matrix for effective security operations center (SOC) analysis. For more in-depth information, refer to the official EC-Council CSA study materials and resources12.

In the context of Cisco ASA Firewall logs, messages are categorized into different severity levels ranging from
0 (emergencies) to 7 (debugging messages). The log entry mentioned specifies a severity level of 5, denoted by "-5-" in the log entry. According to Cisco's documentation, a severity level of 5 corresponds to a
"Notification" level, which indicates a warning condition message. These messages are significant and highlight conditions that could potentially lead to more severe problems if not addressed. The execution of the
'configure term' command by 'enable_15' user, as noted in the log, is an example of a notable event that warrants attention, hence categorized under this severity level.
References:
* "Cisco ASA Series Syslog Messages", Cisco Systems, Inc.
* "Understanding Logging Levels in Cisco ASA Security Appliances", Cisco Community.