Which of the following is a PRIMARY risk that can be introduced through the use of a site-to-site virtual private network (VPN) with a service provider?

A site-to-site VPN extends an organization's trusted network to a service provider, creating a single logical network. The primary risk introduced is the loss of direct control and visibility over the security posture, user activities, and traffic on the provider's side of the connection. The organization's security monitoring tools, such as SIEM and IDS, may not have sensors or log sources within the provider's network. This creates significant blind spots, making it difficult to detect threats or anomalous behavior originating from or passing through the partner network, which is now a trusted extension of the internal environment.

A. Loss of data integrity: VPNs, particularly those using IPsec, are specifically designed to provide data integrity through cryptographic hashing, mitigating this risk rather than introducing it.
C. Data exfiltration: This is a general risk for any network connection. A site-to-site VPN does not uniquely introduce this risk more than other forms of connectivity.
D. Denial of service (DoS) attacks: While the VPN endpoint can be a target, this risk is not unique to connections with service providers and is a general internet-facing threat.

1. NIST Special Publication 800-46 Revision 2, Guide to Enterprise Telework, Remote Access, and Bring Your Own Device (BYOD) Security, Section 4.3.2. It notes that remote access solutions (including site-to-site VPNs) extend the security perimeter, and organizations must consider the security of the remote site, implying a potential lack of visibility and control.

2. Stallings, W. (2017). Cryptography and Network Security: Principles and Practice (7th ed.). Pearson. Chapter 20 discusses IPsec and VPNs, highlighting that while VPNs secure the channel, the security of the connected networks' endpoints and internal activities remains a separate management domain.

3. Carnegie Mellon University, Software Engineering Institute. (2017). Insider Threat Control: Understanding and Mitigating the Risk. The document discusses how trusted business partner connections (like site-to-site VPNs) can become a vector for threats, often due to a lack of visibility into the partner's security practices.