The product 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.
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.

Primary

Unnecessary Complexity

Architecture and Design

Implementation

Operation

Other
Other

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.

The IPSEC specification is complex, which resulted in bugs, partial implementations, and incompatibilities between vendors.

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.

CVE-2007-6067
Support for complex regular expressions leads to a resultant algorithmic complexity weakness (CWE-407).
https://www.cve.org/CVERecord?id=CVE-2007-6067

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).
https://www.cve.org/CVERecord?id=CVE-2007-1552

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.
https://www.cve.org/CVERecord?id=CVE-2007-6479

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.
https://www.cve.org/CVERecord?id=CVE-2005-2148

Allowed-with-Review
This CWE entry is a Class, but it does not have Base-level children.
This entry is classified in a part of CWE's hierarchy that does not have sufficiently low-level coverage, which might reflect a lack of classification-oriented weakness research in the software security community. Conduct careful root cause analysis to determine the original mistake that led to this weakness. If closer analysis reveals that this weakness is appropriate, then this might be the best available CWE to use for mapping. If no other option is available, then it is acceptable to map to this CWE.

Pascal Meunier
Purdue University
2008-01-18
Draft 8
2008-01-30

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Description, Relationships, Weakness_Ordinalities

CWE Content Team
MITRE
2009-01-12
updated Description, Name

CWE Content Team
MITRE
2010-12-13
updated Name, Research_Gaps

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Applicable_Platforms, Causal_Nature

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2022-10-13
updated References

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated References, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Demonstrative_Examples

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Mapping_Notes

David Rothenberg
2024-09-13
4.17
2025-04-03
Suggested changes to the mapping notes.

Design Principle Violation: Not Using Economy of Mechanism
Failure to Use Economy of Mechanism