CWE - CWE-662: Improper Synchronization (4.18)

Home > CWE List > CWE-662: Improper Synchronization (4.18)

CWE Glossary Definition

CWE-662: Improper Synchronization

Weakness ID: 662

Vulnerability Mapping: DISCOURAGED This CWE ID should not be used to map to real-world vulnerabilities
Abstraction: Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.

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Description

The product utilizes multiple threads or processes to allow temporary access to a shared resource that can only be exclusive to one process at a time, but it does not properly synchronize these actions, which might cause simultaneous accesses of this resource by multiple threads or processes.

Extended Description

Synchronization refers to a variety of behaviors and mechanisms that allow two or more independently-operating processes or threads to ensure that they operate on shared resources in predictable ways that do not interfere with each other. Some shared resource operations cannot be executed atomically; that is, multiple steps must be guaranteed to execute sequentially, without any interference by other processes. Synchronization mechanisms vary widely, but they may include locking, mutexes, and semaphores. When a multi-step operation on a shared resource cannot be guaranteed to execute independent of interference, then the resulting behavior can be unpredictable. Improper synchronization could lead to data or memory corruption, denial of service, etc.

Common Consequences

Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Impact	Details
Modify Application Data; Read Application Data; Alter Execution Logic	Scope: Integrity, Confidentiality, Other

Potential Mitigations

Phase(s)	Mitigation
Implementation	Use industry standard APIs to synchronize your code.

Relationships

Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

Relevant to the view "Research Concepts" (View-1000)

Nature	Type	ID	Name
ChildOf	Pillar Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.	664	Improper Control of a Resource Through its Lifetime
ChildOf	Pillar Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.	691	Insufficient Control Flow Management
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	663	Use of a Non-reentrant Function in a Concurrent Context
ParentOf	Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	667	Improper Locking
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	820	Missing Synchronization
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	821	Incorrect Synchronization
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	1058	Invokable Control Element in Multi-Thread Context with non-Final Static Storable or Member Element
CanPrecede	Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	362	Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)

Nature	Type	ID	Name
MemberOf	View View - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).	1003	Weaknesses for Simplified Mapping of Published Vulnerabilities
ParentOf	Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	667	Improper Locking

Relevant to the view "CISQ Quality Measures (2020)" (View-1305)

Nature	Type	ID	Name
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	366	Race Condition within a Thread
ParentOf	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	543	Use of Singleton Pattern Without Synchronization in a Multithreaded Context
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	567	Unsynchronized Access to Shared Data in a Multithreaded Context
ParentOf	Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	667	Improper Locking
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	764	Multiple Locks of a Critical Resource
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	820	Missing Synchronization
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	821	Incorrect Synchronization
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	833	Deadlock
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	1058	Invokable Control Element in Multi-Thread Context with non-Final Static Storable or Member Element
ParentOf	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	1096	Singleton Class Instance Creation without Proper Locking or Synchronization

Relevant to the view "CISQ Data Protection Measures" (View-1340)

Nature	Type	ID	Name
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	366	Race Condition within a Thread
ParentOf	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	543	Use of Singleton Pattern Without Synchronization in a Multithreaded Context
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	567	Unsynchronized Access to Shared Data in a Multithreaded Context
ParentOf	Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	667	Improper Locking
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	764	Multiple Locks of a Critical Resource
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	820	Missing Synchronization
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	821	Incorrect Synchronization
ParentOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	1058	Invokable Control Element in Multi-Thread Context with non-Final Static Storable or Member Element
ParentOf	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	1096	Singleton Class Instance Creation without Proper Locking or Synchronization

Modes Of Introduction

Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Architecture and Design
Implementation

Demonstrative Examples

Example 1

The following function attempts to acquire a lock in order to perform operations on a shared resource.

(bad code)

Example Language: C

void f(pthread_mutex_t *mutex) {

pthread_mutex_lock(mutex);

/* access shared resource */

pthread_mutex_unlock(mutex);

}

However, the code does not check the value returned by pthread_mutex_lock() for errors. If pthread_mutex_lock() cannot acquire the mutex for any reason, the function may introduce a race condition into the program and result in undefined behavior.

In order to avoid data races, correctly written programs must check the result of thread synchronization functions and appropriately handle all errors, either by attempting to recover from them or reporting them to higher levels.

(good code)

Example Language: C

int f(pthread_mutex_t *mutex) {

int result;

result = pthread_mutex_lock(mutex);
if (0 != result)

return result;

/* access shared resource */

return pthread_mutex_unlock(mutex);

}

Example 2

The following code intends to fork a process, then have both the parent and child processes print a single line.

(bad code)

Example Language: C

static void print (char * string) {

char * word;
int counter;
for (word = string; counter = *word++; ) {

putc(counter, stdout);
fflush(stdout);
/* Make timing window a little larger... */

sleep(1);

}

}

int main(void) {

pid_t pid;

pid = fork();
if (pid == -1) {

exit(-2);

}
else if (pid == 0) {

print("child\n");

}
else {

print("PARENT\n");

}
exit(0);

}

One might expect the code to print out something like:

PARENT

child

However, because the parent and child are executing concurrently, and stdout is flushed each time a character is printed, the output might be mixed together, such as:

PcAhRiElNdT

[blank line]

Selected Observed Examples

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Reference	Description
CVE-2021-1782	Chain: improper locking (CWE-667) leads to race condition (CWE-362), as exploited in the wild per CISA KEV.
CVE-2009-0935	Attacker provides invalid address to a memory-reading function, causing a mutex to be unlocked twice

Memberships

Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.

Nature	Type	ID	Name
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	745	CERT C Secure Coding Standard (2008) Chapter 12 - Signals (SIG)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	852	The CERT Oracle Secure Coding Standard for Java (2011) Chapter 9 - Visibility and Atomicity (VNA)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	879	CERT C++ Secure Coding Section 11 - Signals (SIG)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	986	SFP Secondary Cluster: Missing Lock
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1142	SEI CERT Oracle Secure Coding Standard for Java - Guidelines 08. Visibility and Atomicity (VNA)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1166	SEI CERT C Coding Standard - Guidelines 11. Signals (SIG)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1306	CISQ Quality Measures - Reliability
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1308	CISQ Quality Measures - Security
MemberOf	ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).	1340	CISQ Data Protection Measures
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1416	Comprehensive Categorization: Resource Lifecycle Management

Vulnerability Mapping Notes

Usage DISCOURAGED

(this CWE ID should not be used to map to real-world vulnerabilities)

Reason Abstraction

Rationale

This CWE entry is a level-1 Class (i.e., a child of a Pillar). It might have lower-level children that would be more appropriate

Comments

Examine children of this entry to see if there is a better fit

Notes

Maintenance

Deeper research is necessary for synchronization and related mechanisms, including locks, mutexes, semaphores, and other mechanisms. Multiple entries are dependent on this research, which includes relationships to concurrency, race conditions, reentrant functions, etc. CWE-662 and its children - including CWE-667, CWE-820, CWE-821, and others - may need to be modified significantly, along with their relationships.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
CERT C Secure Coding	SIG00-C	Mask signals handled by noninterruptible signal handlers
CERT C Secure Coding	SIG31-C	CWE More Abstract	Do not access shared objects in signal handlers
CLASP	State synchronization error
The CERT Oracle Secure Coding Standard for Java (2011)	VNA03-J	Do not assume that a group of calls to independently atomic methods is atomic
Software Fault Patterns	SFP19	Missing Lock

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-25	Forced Deadlock
CAPEC-26	Leveraging Race Conditions
CAPEC-27	Leveraging Race Conditions via Symbolic Links
CAPEC-29	Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions

Content History

Submissions
Submission Date	Submitter	Organization
2008年04月11日 (CWE Draft 9, 2008年04月11日)	CWE Community
2008年04月11日 (CWE Draft 9, 2008年04月11日)	Submitted by members of the CWE community to extend early CWE versions
Modifications
Modification Date	Modifier	Organization
2024年02月29日 (CWE 4.14, 2024年02月29日)	CWE Content Team	MITRE
2024年02月29日 (CWE 4.14, 2024年02月29日)	updated Mapping_Notes
2023年10月26日	CWE Content Team	MITRE
2023年10月26日	updated Demonstrative_Examples, Observed_Examples
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated Relationships
2023年01月31日	CWE Content Team	MITRE
2023年01月31日	updated Description
2020年12月10日	CWE Content Team	MITRE
2020年12月10日	updated Relationships
2020年08月20日	CWE Content Team	MITRE
2020年08月20日	updated Relationships
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Description, Relationships
2019年09月23日	CWE Content Team	MITRE
2019年09月23日	updated Description, Maintenance_Notes, Relationships
2019年06月20日	CWE Content Team	MITRE
2019年06月20日	updated Type
2019年01月03日	CWE Content Team	MITRE
2019年01月03日	updated Relationships, Taxonomy_Mappings
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Taxonomy_Mappings
2014年07月30日	CWE Content Team	MITRE
2014年07月30日	updated Relationships, Taxonomy_Mappings
2013年07月17日	CWE Content Team	MITRE
2013年07月17日	updated Relationships
2012年10月30日	CWE Content Team	MITRE
2012年10月30日	updated Potential_Mitigations
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Relationships
2011年09月13日	CWE Content Team	MITRE
2011年09月13日	updated Relationships, Taxonomy_Mappings
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences, Relationships, Taxonomy_Mappings
2010年12月13日	CWE Content Team	MITRE
2010年12月13日	updated Description, Relationships, Taxonomy_Mappings
2010年09月27日	CWE Content Team	MITRE
2010年09月27日	updated Name, Relationships
2009年05月27日	CWE Content Team	MITRE
2009年05月27日	updated Relationships
2009年03月10日	CWE Content Team	MITRE
2009年03月10日	updated Related_Attack_Patterns
2008年11月24日	CWE Content Team	MITRE
2008年11月24日	updated Relationships, Taxonomy_Mappings
2008年10月14日	CWE Content Team	MITRE
2008年10月14日	updated Relationships
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Relationships
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Potential_Mitigations, Time_of_Introduction
Previous Entry Names
Change Date	Previous Entry Name
2010年09月27日	Insufficient Synchronization

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Page Last Updated: September 09, 2025

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