Failure to Use Complete Mediation
Weakness ID: 638 (Weakness Class)Status: Draft
+ Description

Description Summary

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.

Extended Description

+ Time of Introduction
  • Architecture and Design
  • Implementation
  • Operation
+ Applicable Platforms



+ Common Consequences

A user might retain access to a critical resource even after privileges have been revoked, possibly allowing access to privileged functionality or sensitive information, depending on the role of the resource.

+ Demonstrative Examples

Example 1

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 2

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.

+ Observed Examples
CVE-2007-0408Server does not properly validate client certificates when reusing cached connections.
+ Potential Mitigations

Invalidate cached privileges, file handles or descriptors, or other access credentials whenever identities, processes, policies, roles, capabilities or permissions change. Perform complete authentication checks before accepting, caching and reusing data, dynamic content and code (scripts). Avoid caching access control decisions as much as possible.

Identify all possible code paths that might access sensitive resources. If possible, create and use a single interface that performs the access checks, and develop code standards that require use of this interface.

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class285Improper Access Control (Authorization)
Research Concepts1000
ChildOfWeakness ClassWeakness Class657Violation of Secure Design Principles
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness ClassWeakness Class424Failure to Protect Alternate Path
Research Concepts (primary)1000
+ Causal Nature


+ Related Attack Patterns
CAPEC-IDAttack Pattern Name
(CAPEC Version: 1.4)
104Cross Zone Scripting
+ References
Jerome H. Saltzer and Michael D. Schroeder. "The Protection of Information in Computer Systems". Proceedings of the IEEE 63. September, 1975. <>.
Sean Barnum and Michael Gegick. "Complete Mediation". 2005-09-12. <>.
+ Content History
Submission DateSubmitterOrganizationSource
2008-01-18Pascal MeunierPurdue UniversityExternal Submission
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Common Consequences, Relationships, Observed Example, Weakness Ordinalities
2009-01-12CWE Content TeamMITREInternal
updated Description, Name
2009-05-27CWE Content TeamMITREInternal
updated Related Attack Patterns
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Design Principle Violation: Not Using Complete Mediation