CWE

Common Weakness Enumeration

A Community-Developed List of Software & Hardware Weakness Types

CWE Top 25 Most Dangerous Weaknesses
Home > CWE List > CWE- Individual Dictionary Definition (4.4)  
ID

CWE-820: Missing Synchronization

Weakness ID: 820
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software utilizes a shared resource in a concurrent manner but does not attempt to synchronize access to the resource.
+ Extended Description
If access to a shared resource is not synchronized, then the resource may not be in a state that is expected by the software. This might lead to unexpected or insecure behaviors, especially if an attacker can influence the shared resource.
+ Relationships

The table(s) below 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" (CWE-1000)
NatureTypeIDName
ChildOfClassClass - 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.662Improper Synchronization
ParentOfVariantVariant - 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.543Use of Singleton Pattern Without Synchronization in a Multithreaded Context
ParentOfBaseBase - 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.567Unsynchronized Access to Shared Data in a Multithreaded Context
ParentOfVariantVariant - 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.1096Singleton Class Instance Creation without Proper Locking or Synchronization
+ Relevant to the view "Software Development" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.557Concurrency Issues
+ Relevant to the view "CISQ Quality Measures (2020)" (CWE-1305)
NatureTypeIDName
ChildOfClassClass - 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.662Improper Synchronization
+ Relevant to the view "CISQ Data Protection Measures" (CWE-1340)
NatureTypeIDName
ChildOfClassClass - 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.662Improper Synchronization
+ Common Consequences

The table below 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.

ScopeImpactLikelihood
Integrity
Confidentiality
Other

Technical Impact: Modify Application Data; Read Application Data; Alter Execution Logic

+ Demonstrative Examples

Example 1

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

(bad code)
Example Language:
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]
[blank line]

+ Memberships
This 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.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.853The CERT Oracle Secure Coding Standard for Java (2011) Chapter 10 - Locking (LCK)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1143SEI CERT Oracle Secure Coding Standard for Java - Guidelines 09. Locking (LCK)
+ 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 NameNode IDFitMapped Node Name
The CERT Oracle Secure Coding Standard for Java (2011)LCK05-JSynchronize access to static fields that can be modified by untrusted code
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2010-08-06CWE Content TeamMITRE
+ Modifications
Modification DateModifierOrganization
2010-12-13CWE Content TeamMITRE
updated Demonstrative_Examples, Relationships
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2013-07-17CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Demonstrative_Examples
2019-01-03CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2019-09-23CWE Content TeamMITRE
updated Maintenance_Notes
2020-02-24CWE Content TeamMITRE
updated Relationships
2020-08-20CWE Content TeamMITRE
updated Relationships
2020-12-10CWE Content TeamMITRE
updated Relationships
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Page Last Updated: March 15, 2021