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NIST SP 800-53 Rev. 5 · SC-7

Boundary Protection

US National Institute of Standards and Technology (NIST) · cited in 821 of our lessons

Explanation

What it asks for. Communications must be monitored and controlled at the external boundary and at key internal boundaries, publicly accessible components must sit in separated subnetworks, and external connections must only go through managed interfaces that follow the security architecture.

In practice. Doing this well means firewalls or cloud security groups with default-deny rules, a segmented zone for internet-facing services, controlled egress, and internal segmentation between user, server and management networks. Auditors expect network diagrams, rule sets with documented business justification, rule review records and evidence of monitoring at boundaries. CIS Control 12 and ISO/IEC 27001 network segregation cover similar ground.

Common gaps. Flat internal networks, permissive outbound rules and firewall rule bases that are never reviewed are typical findings. Cloud environments with many separate entry points often lack a single, managed view of the boundary.

Open SP 800-53 at NIST
The official text
a. Monitor and control communications at the external managed interfaces to the system and at key internal managed interfaces within the system; b. Implement subnetworks for publicly accessible system components that are [Selection: physically; logically] separated from internal organizational networks; and c. Connect to external networks or systems only through managed interfaces consisting of boundary protection devices arranged in accordance with an organizational security and privacy architecture. Discussion: Managed interfaces include gateways, routers, firewalls, guards, network-based malicious code analysis, virtualization systems, or encrypted tunnels implemented within a security architecture. Subnetworks that are physically or logically separated from internal networks are referred to as demilitarized zones or DMZs. Restricting or prohibiting interfaces within organizational systems includes restricting external web traffic to designated web servers within managed interfaces, prohibiting external traffic that appears to be spoofing internal addresses, and prohibiting internal traffic that appears to be spoofing external addresses. [SP 800-189](#f5edfe51-d1f2-422e-9b27-5d0e90b49c72) provides additional information on source address validation techniques to prevent ingress and egress of traffic with spoofed addresses. Commercial telecommunications services are provided by network components and consolidated management systems shared by customers. These services may also include third party-provided access lines and other service elements. Such services may represent sources of increased risk despite contract security provisions. Boundary protection may be implemented as a common control for all or part of an organizational network such that the boundary to be protected is greater than a system-specific boundary (i.e., an authorization boundary).

From NIST SP 800-53 Rev. 5, a work of the US government in the public domain.

Lessons that cite it

Real incidents where this item mattered: the latest 12 of 821.