CWE-609: Double-Checked Locking

Extended Description

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.

Code Examples & CVEs

Demonstrative Examples

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

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.

BadJava

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

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

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.

BadJava

helper = new Helper();

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-609 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-609, Double-Checked Locking, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Double-Checked Locking during Implementation

MITRE associates mitigation with Implementation; documented detection approaches include Automated Static Analysis; recorded impacts include Modify Application Data, and Alter Execution Logic. Use these source-defined anchors to turn CWE-609 into implementation, review, and verification checks for the affected component.

CWE-609: Double-Checked Locking — MITRE CWE

Triage CWE-609 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-609, Double-Checked Locking, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-609

Apply MITRE's full root-cause mapping guidance when using CWE-609, Double-Checked Locking. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-609 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-609, Double-Checked Locking. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-609: Double-Checked Locking?+

CWE-609: Double-Checked Locking is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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.

What are the security consequences of Double-Checked Locking?+

If exploited, CWE-609 (Double-Checked Locking) it can compromise Integrity and Other, leading to outcomes such as Modify Application Data and Alter Execution Logic.

How do you prevent or mitigate Double-Checked Locking?+

Recommended mitigations for CWE-609 include: 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.

Which programming languages are affected by Double-Checked Locking?+

CWE-609 commonly affects Java. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-609 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-609: Double-Checked Locking

Extended Description

Technical Details

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Security Consequences

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