NIST 800-53 REV 5 • SYSTEM AND SERVICES ACQUISITION
SA-8(2) — Least Common Mechanism
Implement the security design principle of least common mechanism in {{ insert: param, sa-08.02_odp }}.
CMMC Practice Mapping
No direct CMMC mapping
NIST 800-171 Mapping
No direct NIST 800-171 mapping
Related Controls
No related controls listed
Supplemental Guidance
The principle of least common mechanism states that the amount of mechanism common to more than one user and depended on by all users is minimized [POPEK74](#79453f84-26a4-4995-8257-d32d37aefea3) . Mechanism minimization implies that different components of a system refrain from using the same mechanism to access a system resource. Every shared mechanism (especially a mechanism involving shared variables) represents a potential information path between users and is designed with care to ensure that it does not unintentionally compromise security [SALTZER75](#c9495d6e-ef64-4090-8509-e58c3b9009ff) . Implementing the principle of least common mechanism helps to reduce the adverse consequences of sharing the system state among different programs. A single program that corrupts a shared state (including shared variables) has the potential to corrupt other programs that are dependent on the state. The principle of least common mechanism also supports the principle of simplicity of design and addresses the issue of covert storage channels [LAMPSON73](#d1cdab13-4218-400d-91a9-c3818dfa5ec8).
Practitioner Notes
Least common mechanism means minimizing the number of shared components between users and systems. Shared mechanisms (shared databases, shared service accounts) create paths for one user to affect another.
Example 1: Avoid shared service accounts — give each service and application its own dedicated credential. If your web app and reporting tool share the same database account, a vulnerability in the reporting tool gives an attacker the same access as the web app. Separate accounts, separate permissions.
Example 2: In cloud environments, avoid shared tenants or shared compute resources for sensitive workloads when possible. Use dedicated Azure subscriptions for different security zones and isolate workloads using separate virtual networks rather than relying solely on security groups within a shared network.