When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions.
By entering a less secure state, the product inherits the weaknesses associated with that state, making it easier to compromise. At the least, it causes administrators to have a false sense of security. This weakness typically occurs as a result of wanting to "fail functional" to minimize administration and support costs, instead of "failing safe."

Primary

Failing Open

Architecture and Design

Implementation

Access Control
Bypass Protection Mechanism
Intended access restrictions can be bypassed, which is often contradictory to what the product's administrator expects.

Architecture and Design
Subdivide and allocate resources and components so that a failure in one part does not affect the entire product.

Switches may revert their functionality to that of hubs when the table used to map ARP information to the switch interface overflows, such as when under a spoofing attack. This results in traffic being broadcast to an eavesdropper, instead of being sent only on the relevant switch interface. To mitigate this type of problem, the developer could limit the number of ARP entries that can be recorded for a given switch interface, while other interfaces may keep functioning normally. Configuration options can be provided on the appropriate actions to be taken in case of a detected failure, but safe defaults should be used.

CVE-2007-5277
The failure of connection attempts in a web browser resets DNS pin restrictions. An attacker can then bypass the same origin policy by rebinding a domain name to a different IP address. This was an attempt to "fail functional."
https://www.cve.org/CVERecord?id=CVE-2007-5277

CVE-2006-4407
Incorrect prioritization leads to the selection of a weaker cipher. Although it is not known whether this issue occurred in implementation or design, it is feasible that a poorly designed algorithm could be a factor.
https://www.cve.org/CVERecord?id=CVE-2006-4407

A7
Improper Error Handling
CWE More Specific

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

Since design issues are hard to fix, they are rarely publicly reported, so there are few CVE examples of this problem as of January 2008. Most publicly reported issues occur as the result of an implementation error instead of design, such as CVE-2005-3177 (Improper handling of large numbers of resources) or CVE-2005-2969 (inadvertently disabling a verification step, leading to selection of a weaker protocol).

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 Common_Consequences, Description, Name, Relationships, Taxonomy_Mappings, Weakness_Ordinalities

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

CWE Content Team
MITRE
2009-03-10
updated Relationships

CWE Content Team
MITRE
2009-05-27
updated Name

CWE Content Team
MITRE
2010-12-13
updated 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, Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2022-04-28
updated Relationships

CWE Content Team
MITRE
2022-10-13
updated References

CWE Content Team
MITRE
2023-01-31
updated Applicable_Platforms

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
2025-12-11
4.19
2025-12-11
updated Relationships

Design Principle Violation: Not Failing Securely
Design Principle Violation: Not Failing Securely (aka 'Failing Open')
Not Failing Securely (aka 'Failing Open')