This event category is exploitation because the HTTP requests contain PHP code that attempts to execute commands on the web server and create a backdoor. Exploitation is the phase of the attack where the threat actor gains access to the target system and executes malicious code. References: https://learningnetworkstore.
cisco.com/on-demand-e-learning/understanding-cisco-cybersecurity-operations-fundamentals-cbrops-v1-0
/CSCU-LP-CBROPS-V1-028093.html (Module 2, Lesson 2.1.3)

Phishing is considered a low-bandwidth attack because it does not require the use of significant network resources. Instead, it relies on social engineering to deceive individuals into providing sensitive information or clicking on malicious links, often through email or other communication methods1.

The weaponization step in the Cyber Kill Chain model involves creating or repurposing malware based on the information gathered during reconnaissance to exploit vulnerabilities in the target's system. This step culminates in the preparation of the malware to be delivered to the victim2.

The source IP address from an audit log that indicates a session which may have exploited a vulnerability is considered corroborative evidence. This type of evidence supports other evidence that suggests a security breach occurred. In the context of cybersecurity, corroborative evidence can help establish that an attack was carried out and can be used in conjunction with other data points to build a case during an investigation.
References := The Understanding Cisco Cybersecurity Operations Fundamentals (CBROPS) training material discusses the types of data needed to investigate security incidents, which includes understanding the role of different types of evidence in building a security incident case1.

Statistical detection involves collecting data over time to define what is considered normal behavior or legitimate data for users or systems. It then uses statistical analysis to identify abnormal behavior that could indicate a security incident. Rule-based detection uses predefined rules or patterns that are based on known threats or vulnerabilities - it operates on an IF/THEN basis where if certain conditions are met then an alert is triggered. References := Cisco Cybersecurity Operations Fundamentals