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Not Failing Securely ('Failing Open')

ID: 636Date: (C)2012-05-14   (M)2012-11-08
Type: weaknessStatus: DRAFT
Abstraction Type: Class


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.

Extended Description

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."

Applicable Platforms
Language Class: All

Time Of Introduction

  • Architecture and Design
  • Implementation

Common Consequences

ScopeTechnical ImpactNotes
Bypass protection mechanism
Intended access restrictions can be bypassed, which is often contradictory to what the product's administrator expects.

Detection Methods

Potential Mitigations

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


Related CWETypeViewChain
CWE-636 ChildOf CWE-889 Category CWE-888  

Demonstrative Examples   (Details)

  1. 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.

Observed Examples

  1. 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."
  2. 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.

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

White Box Definitions

Black Box Definitions

Taxynomy Mappings

OWASP Top Ten 2004 A7
Improper Error Handling


  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 .Failing Securely. Published on 2005-12-05.

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