Missing Default Case in Switch Statement
Weakness ID: 478 (Weakness Variant)Status: Draft
+ Description

Description Summary

The code does not have a default case in a switch statement, which might lead to complex logical errors and resultant weaknesses.
+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

C

C++

Java

.NET

+ Common Consequences
ScopeEffect
Other

Depending on the logical circumstances involved, any consequences may result: e.g., issues of confidentiality, authentication, authorization, availability, integrity, accountability, or non-repudiation.

+ Demonstrative Examples

Example 1

The following fails to properly check the return code in the case where the security_check function returns a -1 value when an error occurs. If an attacker can supply data that will invoke an error, the attacker can bypass the security check:

(Bad Code)
Example Language: C 
#define FAILED 0
#define PASSED 1
int result;
...
result = security_check(data);
switch (result) {
case FAILED:
printf("Security check failed!\n");
exit(-1);
case PASSED:
printf("Security check passed.\n");
break;
}
// program execution continues...
...

Instead a default label should be used for unaccounted conditions:

(Good Code)
Example Language: C 
#define FAILED 0
#define PASSED 1
int result;
...
result = security_check(data);
switch (result) {
case FAILED:
printf("Security check failed!\n");
exit(-1);
case PASSED:
printf("Security check passed.\n");
break;
default:
printf("Unknown error (%d), exiting...\n",result);
exit(-1);
}

This label is used because the assumption cannot be made that all possible cases are accounted for. A good practice is to reserve the default case for error handling.

+ Potential Mitigations

Phase: Implementation

Ensure that there are no unaccounted for cases, when adjusting flow or values based on the value of a given variable. In switch statements, this can be accomplished through the use of the default label.

+ Other Notes

This flaw represents a common problem in software development, in which not all possible values for a variable are considered or handled by a given process. Because of this, further decisions are made based on poor information, and cascading failure results. This cascading failure may result in any number of security issues, and constitutes a significant failure in the system. In the case of switch style statements, the very simple act of creating a default case can mitigate this situation, if done correctly. Often however, the default cause is used simply to represent an assumed option, as opposed to working as a sanity check. This is poor practice and in some cases is as bad as omitting a default case entirely.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory171Cleansing, Canonicalization, and Comparison Errors
Development Concepts699
ChildOfWeakness ClassWeakness Class398Indicator of Poor Code Quality
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class697Insufficient Comparison
Research Concepts (primary)1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPFailure to account for default case in switch
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
CLASPExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable Platforms, Common Consequences, Description, Relationships, Other Notes, Taxonomy Mappings, Weakness Ordinalities
2009-05-27CWE Content TeamMITREInternal
updated Description, Name
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Failure to Account for Default Case in Switch
2009-05-27Failure to Use Default Case in Switch
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