Hardening the engineering workstations using a consistent strategy would have the greatest impact on reducing the attack surface. The workstations are running outdated and unsupported operating systems, with no security controls, and inconsistent software installations, which significantly increases the risk of exploitation. Hardening involves applying patches, reducing unnecessary software, disabling unused services, and ensuring uniform security controls across all systems. By addressing these vulnerabilities and inconsistencies, the overall security posture improves significantly, which aligns with CASP+ best practices on reducing attack surfaces by standardizing and securing endpoint configurations.
Reference:
CASP+ CAS-004 Exam Objectives: Domain 1.0 - Risk Management (Vulnerability Management, System Hardening) CompTIA CASP+ Study Guide: Hardening Techniques and Attack Surface Reduction