Not Using Complete Mediation

The software does not perform access checks on a resource every time the resource is accessed by an entity, which can create resultant weaknesses if that entity's rights or privileges change over time.


Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

When executable library files are used on web servers, which is common in PHP applications, the developer might perform an access check in any user-facing executable, and omit the access check from the library file itself. By directly requesting the library file (CWE-425), an attacker can bypass this access check.

Example Two

When a developer begins to implement input validation for a web application, often the validation is performed in each area of the code that uses externally-controlled input. In complex applications with many inputs, the developer often misses a parameter here or a cookie there. One frequently-applied solution is to centralize all input validation, store these validated inputs in a separate data structure, and require that all access of those inputs must be through that data structure. An alternate approach would be to use an external input validation framework such as Struts, which performs the validation before the inputs are ever processed by the code.

See Also

SFP Secondary Cluster: Race Condition Window

This category identifies Software Fault Patterns (SFPs) within the Race Condition Window cluster (SFP20).

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

Weaknesses Introduced During Design

This view (slice) lists weaknesses that can be introduced during design.


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