NIST 800-53 REV 5 • SYSTEM AND COMMUNICATIONS PROTECTION
SC-7(10) — Prevent Exfiltration
Prevent the exfiltration of information; and Conduct exfiltration tests {{ insert: param, sc-07.10_odp }}.
Supplemental Guidance
Prevention of exfiltration applies to both the intentional and unintentional exfiltration of information. Techniques used to prevent the exfiltration of information from systems may be implemented at internal endpoints, external boundaries, and across managed interfaces and include adherence to protocol formats, monitoring for beaconing activity from systems, disconnecting external network interfaces except when explicitly needed, employing traffic profile analysis to detect deviations from the volume and types of traffic expected, call backs to command and control centers, conducting penetration testing, monitoring for steganography, disassembling and reassembling packet headers, and using data loss and data leakage prevention tools. Devices that enforce strict adherence to protocol formats include deep packet inspection firewalls and Extensible Markup Language (XML) gateways. The devices verify adherence to protocol formats and specifications at the application layer and identify vulnerabilities that cannot be detected by devices that operate at the network or transport layers. The prevention of exfiltration is similar to data loss prevention or data leakage prevention and is closely associated with cross-domain solutions and system guards that enforce information flow requirements.
Practitioner Notes
Data exfiltration prevention means stopping sensitive data from leaving your network through unauthorized channels — encrypted tunnels, steganography, covert channels, or simple file uploads to cloud storage.
Example 1: Deploy a Data Loss Prevention (DLP) solution at your network boundary that inspects outbound traffic for patterns matching CUI, PII, or other sensitive data. Microsoft Purview DLP can scan outbound email and file uploads and block transfers that violate your policies.
Example 2: On your firewall, block outbound DNS over HTTPS (DoH) and DNS over TLS (DoT) to prevent DNS tunneling as an exfiltration channel. Force all DNS through your internal DNS servers where you can monitor queries for suspicious patterns like unusually long subdomain names.