CWE

Unnecessary Complexity in Protection Mechanism (Not Using 'Economy of Mechanism')

ID: 637		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: DRAFT
Abstraction Type: Class

Description

The software uses a more complex mechanism than necessary, which could lead to resultant weaknesses when the mechanism is not correctly understood, modeled, configured, implemented, or used.

Extended Description

Security mechanisms should be as simple as possible. Complex security mechanisms may engender partial implementations and compatibility problems, with resulting mismatches in assumptions and implemented security. A corollary of this principle is that data specifications should be as simple as possible, because complex data specifications result in complex validation code. Complex tasks and systems may also need to be guarded by complex security checks, so simple systems should be preferred.

Applicable Platforms
Language Class: All

Time Of Introduction

• Architecture and Design
• Implementation
• Operation

Common Consequences

Scope	Technical Impact	Notes
Other	Other

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
Architecture and Design		Avoid complex security mechanisms when simpler ones would meet requirements. Avoid complex data models, and unnecessarily complex operations. Adopt architectures that provide guarantees, simplify understanding through elegance and abstraction, and that can be implemented similarly. Modularize, isolate and do not trust complex code, and apply other secure programming principles on these modules (e.g., least privilege) to mitigate vulnerabilities.

Relationships

Related CWE	Type	View	Chain
CWE-637 ChildOf CWE-907	Category	CWE-888

Demonstrative Examples   (Details)

1. HTTP Request Smuggling (CWE-444) attacks are feasible because there are not stringent requirements for how illegal or inconsistent HTTP headers should be handled. This can lead to inconsistent implementations in which a proxy or firewall interprets the same data stream as a different set of requests than the end points in that stream.
2. The IPSEC specification is complex, which resulted in bugs, partial implementations, and incompatibilities between vendors.

Observed Examples

1. CVE-2007-6067 : Support for complex regular expressions leads to a resultant algorithmic complexity weakness (CWE-407).
2. CVE-2007-1552 : Either a filename extension and a Content-Type header could be used to infer the file type, but the developer only checks the Content-Type, enabling unrestricted file upload (CWE-434).
3. CVE-2007-6479 : In Apache environments, a "filename.php.gif" can be redirected to the PHP interpreter instead of being sent as an image/gif directly to the user. Not knowing this, the developer only checks the last extension of a submitted filename, enabling arbitrary code execution.
4. CVE-2005-2148 : The developer cleanses the $_REQUEST superglobal array, but PHP also populates $_GET, allowing attackers to bypass the protection mechanism and conduct SQL injection attacks against code that uses $_GET.

For more examples, refer to CVE relations in the bottom box.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings
None

References:

1. Jerome H. Saltzer Michael D. Schroeder .The Protection of Information in Computer Systems. Proceedings of the IEEE 63. Published on September, 1975.
2. Sean Barnum Michael Gegick .Economy of Mechanism. Published on 2005-09-13.