The product uses double-checked locking to access a resource without the overhead of explicit synchronization, but the locking is insufficient.
Double-checked locking refers to the situation where a programmer checks to see if a resource has been initialized, grabs a lock, checks again to see if the resource has been initialized, and then performs the initialization if it has not occurred yet. This should not be done, as it is not guaranteed to work in all languages and on all architectures. In summary, other threads may not be operating inside the synchronous block and are not guaranteed to see the operations execute in the same order as they would appear inside the synchronous block.

Primary

Implementation

Integrity
Other
Modify Application Data
Alter Execution Logic

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Implementation
While double-checked locking can be achieved in some languages, it is inherently flawed in Java before 1.5, and cannot be achieved without compromising platform independence. Before Java 1.5, only use of the synchronized keyword is known to work. Beginning in Java 1.5, use of the "volatile" keyword allows double-checked locking to work successfully, although there is some debate as to whether it achieves sufficient performance gains. See references.

It may seem that the following bit of code achieves thread safety while avoiding unnecessary synchronization...

if (helper == null) {
synchronized (this) {if (helper == null) {helper = new Helper();}}
}return helper;

The programmer wants to guarantee that only one Helper() object is ever allocated, but does not want to pay the cost of synchronization every time this code is called.
Suppose that helper is not initialized. Then, thread A sees that helper==null and enters the synchronized block and begins to execute:

helper = new Helper();

If a second thread, thread B, takes over in the middle of this call and helper has not finished running the constructor, then thread B may make calls on helper while its fields hold incorrect values.

LCK10-J
Do not use incorrect forms of the double-checked locking idiom

SFP19
Missing Lock

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Anonymous Tool Vendor (under NDA)
2007-05-07
Draft 6
2007-05-07

Eric Dalci
Cigital
2008-07-01
updated Context_Notes

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

CWE Content Team
MITRE
2008-11-24
updated Demonstrative_Examples

CWE Content Team
MITRE
2009-01-12
updated Relationships

CWE Content Team
MITRE
2009-05-27
updated Relationships

CWE Content Team
MITRE
2009-10-29
updated Taxonomy_Mappings

CWE Content Team
MITRE
2010-12-13
updated Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples, References, Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

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

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Detection_Factors, Weakness_Ordinalities

Double Checked Locking