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CWE-543: Use of Singleton Pattern Without Synchronization in a Multithreaded Context

Weakness ID: 543
Abstraction: Variant
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software uses the singleton pattern when creating a resource within a multithreaded environment.

Extended Description

The use of a singleton pattern may not be thread-safe.

+ Time of Introduction
  • Implementation
+ Applicable Platforms




+ Common Consequences

Technical Impact: Other; Modify application data

+ Demonstrative Examples

Example 1

This method is part of a singleton pattern, yet the following singleton() pattern is not thread-safe. It is possible that the method will create two objects instead of only one.

(Bad Code)
Example Language: Java 
private static NumberConverter singleton;
public static NumberConverter get_singleton() {
if (singleton == null) {
singleton = new NumberConverter();
return singleton;

Consider the following course of events:

  • Thread A enters the method, finds singleton to be null, begins the NumberConverter constructor, and then is swapped out of execution.

  • Thread B enters the method and finds that singleton remains null. This will happen if A was swapped out during the middle of the constructor, because the object reference is not set to point at the new object on the heap until the object is fully initialized.

  • Thread B continues and constructs another NumberConverter object and returns it while exiting the method.

  • Thread A continues, finishes constructing its NumberConverter object, and returns its version.

At this point, the threads have created and returned two different objects.

+ Potential Mitigations

Phase: Architecture and Design

Use the Thread-Specific Storage Pattern. See References.

Phase: Implementation

Do not use member fields to store information in the Servlet. In multithreading environments, storing user data in Servlet member fields introduces a data access race condition.

Phase: Implementation

Avoid using the double-checked locking pattern in language versions that cannot guarantee thread safety. This pattern may be used to avoid the overhead of a synchronized call, but in certain versions of Java (for example), this has been shown to be unsafe because it still introduces a race condition (CWE-209).

Effectiveness: Limited

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory381J2EE Time and State Issues
Development Concepts699
ChildOfWeakness BaseWeakness Base820Missing Synchronization
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory861CERT Java Secure Coding Section 49 - Miscellaneous (MSC)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory986SFP Secondary Cluster: Missing Lock
Software Fault Pattern (SFP) Clusters (primary)888
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CERT Java Secure CodingMSC07-JPrevent multiple instantiations of singleton objects
Software Fault PatternsSFP19Missing Lock
+ References
Douglas C. Schmidt, Timothy H. Harrison and Nat Pryce. "Thread-Specifc Storage for C/C++". <>.
+ Content History
Submission DateSubmitterOrganizationSource
Anonymous Tool Vendor (under NDA)Externally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2010-09-27CWE Content TeamMITREInternal
updated Name
2010-12-13CWE Content TeamMITREInternal
updated Applicable_Platforms, Demonstrative_Examples, Description, Potential_Mitigations, References, Relationships, Taxonomy_Mappings
2011-03-29CWE Content TeamMITREInternal
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2010-09-27Use of Singleton Pattern in a Non-thread-safe Manner

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Page Last Updated: May 05, 2017