The SIEM events show that powershell.exe was executed on multiple endpoints with an outbound connection to 40.90.23.154, which is an IP address associated with malicious activity. This could indicate a malware infection or a command-and-control channel. The best response action is to configure the forward proxy to block 40.90.23.154, which would prevent further communication with the malicious IP address. Disabling powershell.exe on all endpoints may not be feasible or effective, as it could affect legitimate operations and not remove the malware. Restarting Microsoft Windows Defender may not detect or stop the malware, as it could have bypassed or disabled it. Disabling local administrator privileges on the endpoints may not prevent the malware from running or communicating, as it could have escalated privileges or used other methods.
Verified References: https://www.comptia.org/blog/what-is-a-forward-proxy https://partners.comptia.org/docs
/default-source/resources/casp-content-guide

A next-generation firewall (NGFW) is a device or software that provides advanced network security features beyond the traditional firewall functions. A NGFW can provide the following capabilities:
Recognize and block fake websites, using URL filtering and reputation-based analysis Decrypt and scan encrypted traffic on standard and non-standard ports, using SSL/TLS inspection and deep packet inspection Use multiple engines for detection and prevention, such as antivirus, intrusion prevention system (IPS), application control, and sandboxing Have central reporting, using a unified management console and dashboard A cloud access security broker (CASB) is a device or software that acts as an intermediary between cloud service users and cloud service providers. A CASB can provide various security functions such as visibility, compliance, data security, and threat protection, but it does not provide all the capabilities of a NGFW. Web filtering is a technique that blocks or allows web access based on predefined criteria such as categories, keywords, or reputation. Web filtering can help recognize and block fake websites, but it does not provide all the capabilities of a NGFW. Endpoint detection and response (EDR) is a technology that monitors and analyzes the activity and behavior of endpoints such as computers or mobile devices. EDR can help detect and respond to advanced threats, but it does not provide all the capabilities of a NGFW. Reference: [CompTIA Advanced Security Practitioner (CASP+) Certification Exam Objectives], Domain 2: Enterprise Security Architecture, Objective 2.2: Select appropriate hardware and software solutions