Use of a Non-reentrant Function in a Concurrent Context (4.19.1)

Weakness ID: 663

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: 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.

Description

The product calls a non-reentrant function in a concurrent context in which a competing code sequence (e.g. thread or signal handler) may have an opportunity to call the same function or otherwise influence its state.

Common Consequences

Section Help This 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 Memory; Read Memory; Modify Application Data; Read Application Data; Alter Execution Logic	Scope: Integrity, Confidentiality, Other

Potential Mitigations

Phase(s)	Mitigation
Implementation	Use reentrant functions if available.
Implementation	Add synchronization to your non-reentrant function.
Implementation	In Java, use the ReentrantLock Class.

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	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.	662	Improper Synchronization
ParentOf	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.	479	Signal Handler Use of a Non-reentrant Function
ParentOf	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.	558	Use of getlogin() in Multithreaded Application
PeerOf	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.	1265	Unintended Reentrant Invocation of Non-reentrant Code Via Nested Calls

Relevant to the view "Software Development" (View-699)

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	557	Concurrency Issues

Modes Of Introduction

Section Help The 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
Implementation

Applicable Platforms

Section Help This listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

C (Undetermined Prevalence)

Demonstrative Examples

Example 1

In this example, a signal handler uses syslog() to log a message:

(bad code)

Example Language: C

char *message;
void sh(int dummy) {

syslog(LOG_NOTICE,"%s\n",message);
sleep(10);
exit(0);

}
int main(int argc,char* argv[]) {

...
signal(SIGHUP,sh);
signal(SIGTERM,sh);
sleep(10);
exit(0);

}

If the execution of the first call to the signal handler is suspended after invoking syslog(), and the signal handler is called a second time, the memory allocated by syslog() enters an undefined, and possibly, exploitable state.

Example 2

The following code relies on getlogin() to determine whether or not a user is trusted. It is easily subverted.

(bad code)

Example Language: C

pwd = getpwnam(getlogin());
if (isTrustedGroup(pwd->pw_gid)) {

allow();

} else {

deny();

}

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-2001-1349	unsafe calls to library functions from signal handler
CVE-2004-2259	SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.

Weakness Ordinalities

Ordinality	Description
Primary	(where the weakness exists independent of other weaknesses)

Detection Methods

Method	Details
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.) Effectiveness: High

Method

Details

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.)

Effectiveness: High

Memberships

Section Help 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.

Vulnerability Mapping Notes

Usage	ALLOWED (this CWE ID may be used to map to real-world vulnerabilities)
Reason	Acceptable-Use
Rationale	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.
Comments	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.

References

Content History

Submissions
Submission Date	Submitter	Organization
2008-04-11 (CWE Draft 9, 2008-04-11)	CWE Community
2008-04-11 (CWE Draft 9, 2008-04-11)	Submitted by members of the CWE community to extend early CWE versions
Modifications
Modification Date	Modifier	Organization
2025-12-11 (CWE 4.19, 2025-12-11)	CWE Content Team	MITRE
2025-12-11 (CWE 4.19, 2025-12-11)	updated Applicable_Platforms, Detection_Factors, Weakness_Ordinalities
2025-04-03 (CWE 4.17, 2025-04-03)	CWE Content Team	MITRE
2025-04-03 (CWE 4.17, 2025-04-03)	updated Demonstrative_Examples
2023-10-26	CWE Content Team	MITRE
2023-10-26	updated Demonstrative_Examples
2023-06-29	CWE Content Team	MITRE
2023-06-29	updated Mapping_Notes
2023-04-27	CWE Content Team	MITRE
2023-04-27	updated References, Relationships, Time_of_Introduction
2023-01-31	CWE Content Team	MITRE
2023-01-31	updated Description
2020-12-10	CWE Content Team	MITRE
2020-12-10	updated Common_Consequences
2020-06-25	CWE Content Team	MITRE
2020-06-25	updated Relationships
2020-02-24	CWE Content Team	MITRE
2020-02-24	updated Relationships
2017-11-08	CWE Content Team	MITRE
2017-11-08	updated Observed_Examples
2014-07-30	CWE Content Team	MITRE
2014-07-30	updated Relationships
2012-05-11	CWE Content Team	MITRE
2012-05-11	updated Relationships
2011-06-01	CWE Content Team	MITRE
2011-06-01	updated Common_Consequences
2010-12-13	CWE Content Team	MITRE
2010-12-13	updated Description, Name, Relationships
2010-09-27	CWE Content Team	MITRE
2010-09-27	updated Name, Observed_Examples, Potential_Mitigations, References, Relationships
2009-03-10	CWE Content Team	MITRE
2009-03-10	updated Related_Attack_Patterns
2008-09-08	CWE Content Team	MITRE
2008-09-08	updated Relationships, References
2008-07-01	Eric Dalci	Cigital
2008-07-01	updated References, Potential_Mitigations, Time_of_Introduction
Previous Entry Names
Change Date	Previous Entry Name
2010-09-27	Use of a Non-reentrant Function in an Unsynchronized Context
2010-12-13	Use of a Non-reentrant Function in a Multithreaded Context