According to the NIST SP 800-61 incident handling process, the SOC team should first isolate the affected endpoints to prevent further spread of the attack and take disk images for analysis (A). This helps in preserving evidence for a thorough investigation. The next step would be to block the connection to the C&C server on the perimeter next-generation firewall , which helps to cut off the communication between the compromised endpoint and the attacker's server, thereby mitigating the threat123.
References: The answers are based on the guidelines provided in the NIST SP 800-61 Computer Security Incident Handling Guide, which outlines the steps for incident handling, including detection, analysis, containment, eradication, recovery, and post-incident activities