Complete Mediation¶

Every access to every resource must be checked for authorization; caching authorization decisions creates time-of-check to time-of-use vulnerabilities.

Tension Addressed¶

Security vs. Performance

Recognizable As¶

Authorization checks on every request (not just first); capability-based security; reference monitors; access control lists checked at access time; session validation on every operation.

Canonical Sources¶

Saltzer & Schroeder, "The Protection of Information in Computer Systems" (1975); Anderson, "Computer Security Technology Planning Study" (1972)

Transfers To¶

Physical security (checking credentials at every door), financial transactions (per-transaction authorization), API gateways (per-request validation)

Performance pressure creates temptation to cache authorization decisions, but permissions can change between the check and the use.