CISA conducted a SILENTSHIELD assessment on a Federal Civilian Executive Branch organization, simulating nation-state cyber operations. The red team gained initial access through an unpatched web server vulnerability and then compromised the Windows network via phishing. The team fully compromised the domain and pivoted to an external organization, highlighting the importance of defense-in-depth. The organization had insufficient controls to prevent and detect malicious activity, inefficient log collection and analysis, and bureaucratic barriers hindering network defenders. The team's findings emphasized the value of behavior-based indicators of compromise, an "allowlist" approach, and defense-in-depth. CISA recommends applying these principles, including robust network segmentation, baselining network traffic, and focusing on behavior-based detection. Software manufacturers are urged to implement secure by design principles and eliminate default passwords to enhance network security. By addressing these vulnerabilities, organizations can reduce the risk of domain compromise and malicious cyber activity.