Spoofing, tampering, repudiation, information disclosure, denial of service, and elevation of privilege are part of a known threat modeling method called STRIDE. STRIDE is a mnemonic that stands for six categories of threats that can affect the security of a system or application. STRIDE was developed by Microsoft in 1999 and has been widely adopted as a threat modeling method by many organizations. STRIDE can help identify and prioritize potential threats based on their impact and likelihood1.

A communications plan is a document that outlines who should be notified and how during an incident response. It can also specify the roles and responsibilities of the incident response team members, the escalation procedures, and the communication channels. Consulting the communications plan is the most appropriate next step in an incident response plan after determining a security incident has occurred. Consulting the malware analysis process, the disaster recovery plan, or the data classification process may be relevant at later stages of the incident response, but not as the next step. Reference: https://www.sans.org/reading-room/whitepapers/incident/incident-handlers-handbook-33901

The security analyst should review the IDS rule set first. The IDS (Intrusion Detection System) is a tool that monitors network traffic and alerts on any suspicious or malicious activity. The IDS rule set is a set of conditions or patterns that define what constitutes normal or abnormal behavior on the network. The IDS rule set can affect the number of security incidents being reported, as it determines what triggers an alert or not3. The security analyst should review the IDS rule set to check if it is up to date, accurate, and comprehensive. If the IDS rule set is outdated, inaccurate, or incomplete, it may miss some incidents or generate false positives or negatives.

The security analyst should review the known Apache vulnerabilities to determine if a compromise actually occurred. The SIEM alert indicates that an IDS signature detected an attempt to exploit a vulnerability in Apache Struts 2 (CVE-2017-5638), which allows remote code execution via a crafted Content-Type header4. The packet capture and TCP stream show that the attacker sent a malicious request with a Content-Type header containing an OGNL expression that executes the command "whoami" on the target server. However, this does not necessarily mean that the attack was successful, as it depends on whether the target server was running a vulnerable version of Apache Struts 2 or not. Therefore, the security analyst should review the known Apache vulnerabilities and compare them with the version of Apache Struts 2 running on the server to confirm if a compromise actually occurred or not.

A port scan generated the output. A port scan is a type of attack that probes a host or a network for open ports or services. A port scan can help an attacker discover potential vulnerabilities or entry points for further exploitation. The output shows that tcpdump captured packets with different flags, such as SYN, ACK, RST, and FIN, which indicate different stages of the TCP three-way handshake or connection termination. The output also shows that the source IP address 192.168.1.100 sent packets to different destination ports on the target IP address 192.168.1.101, such as 22, 23, 25, 80, and 443. These are common ports that an attacker would scan to find out what services are running on the target.