Risk mitigation involves taking actions to reduce either the likelihood or impact of a threat. By implementing a firewall between the two environments, Company A is minimizing the risk of threats from Company B impacting its own systems. Accepting the risk would involve taking no action, avoiding it would mean terminating activities with Company B, and transferring would involve outsourcing the risk, none of which occurred here.
Reference:CompTIA SecurityX CAS-005, Domain 1.0: Apply appropriate risk response techniques to identified risks.

DomainKeys Identified Mail (DKIM) digitally signs outbound messages with the organization's private key, enabling recipients to verify integrity and authenticity using the corresponding public key in DNS.
SPF validates sending server IPs, not message integrity.
DMARC builds policy enforcement on top of SPF and DKIM results.
TLS secures the transport channel, not the message content itself.

The best solution is to use a non-persistent virtual desktop infrastructure (VDI) with thin clients (B). Thin clients are inexpensive, easy to replace, and resilient in harsh environments where traditional endpoints may be damaged. With non-persistent VDI, employee desktops are virtualized and reset to a clean state after logout, reducing risks from turnover, malware persistence, or user misconfiguration. Centralized management ensures consistent patching and security updates while minimizing downtime, since damaged thin clients can be swapped quickly with minimal disruption.
Option A (environmental controls) may reduce equipment damage but does not address turnover or regulatory retention requirements. Option C (redundant servers and journaling) improves data integrity but does not solve endpoint-related risks or staffing issues. Option D (maintaining spare endpoints) mitigates hardware failures but still relies on managing and configuring full systems, which is inefficient for high-turnover environments.
CAS-005 emphasizes virtualization and centralization strategies in environments where operational resilience, rapid recovery, and compliance are critical. Non-persistent VDI with thin clients provides the most comprehensive solution here.

In a federated environment divided by region, if user identities are not synchronized across regions, authentication may be slow or fail when employees travel. CAS-005 IAM guidance states that identity synchronization ensures user attributes and credentials are consistently available in all regions, reducing latency and login issues.
* Option A creates separate identities, which breaks single identity management.
* Option C is unrelated to the login performance issue.
* Option D may resolve SSO appliance sync but not cross-region identity data availability.

Implementing digital signatures ensures the integrity and authenticity of software binaries. When a binary is digitally signed, any tampering with the file (e.g., replacing it with a malicious version) would invalidate the signature. This allows systems to verify the origin and integrity of binaries before execution, preventing the execution of unauthorized or compromised binaries.
* A. Improving patching processes: While important, this does not directly address the issue of verifying the integrity of binaries.
* B. Implementing digital signatures: This ensures that only valid, untampered binaries are executed, preventing attackers from substituting legitimate binaries with malicious ones.
* C. Performing manual updates via USB ports: This is not practical and does not scale well, especially in large environments.
* D. Allowing only files from internal sources: This reduces the risk but does not provide a mechanism to verify the integrity of binaries.
References:
* CompTIA Security+ Study Guide
* NIST SP 800-57, "Recommendation for Key Management"
* OWASP (Open Web Application Security Project) guidelines on code signing