CWE - CWE-479: Signal Handler Use of a Non-reentrant Function (4.17)

Weakness ID: 479

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

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Description

The product defines a signal handler that calls a non-reentrant function.

Extended Description

Non-reentrant functions are functions that cannot safely be called, interrupted, and then recalled before the first call has finished without resulting in memory corruption. This can lead to an unexpected system state and unpredictable results with a variety of potential consequences depending on context, including denial of service and code execution.

Many functions are not reentrant, but some of them can result in the corruption of memory if they are used in a signal handler. The function call syslog() is an example of this. In order to perform its functionality, it allocates a small amount of memory as "scratch space." If syslog() is suspended by a signal call and the signal handler calls syslog(), the memory used by both of these functions enters an undefined, and possibly, exploitable state. Implementations of malloc() and free() manage metadata in global structures in order to track which memory is allocated versus which memory is available, but they are non-reentrant. Simultaneous calls to these functions can cause corruption of the metadata.

Common Consequences

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
Execute Unauthorized Code or Commands	Scope: Integrity, Confidentiality, Availability It may be possible to execute arbitrary code through the use of a write-what-where condition.
Modify Memory; Modify Application Data	Scope: Integrity Signal race conditions often result in data corruption.

Potential Mitigations

Phase(s)	Mitigation
Requirements	Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness.
Architecture and Design	Design signal handlers to only set flags rather than perform complex functionality.
Implementation	Ensure that non-reentrant functions are not found in signal handlers.
Implementation	Use sanity checks to reduce the timing window for exploitation of race conditions. This is only a partial solution, since many attacks might fail, but other attacks still might work within the narrower window, even accidentally. Effectiveness: Defense in Depth

Relationships

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	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
ChildOf	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.	828	Signal Handler with Functionality that is not Asynchronous-Safe
CanPrecede	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.	123	Write-what-where Condition

Modes Of Introduction

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

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

C (Undetermined Prevalence)

C++ (Undetermined Prevalence)

Likelihood Of Exploit

Low

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.

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-2005-0893	signal handler calls function that ultimately uses malloc()
CVE-2004-2259	SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.

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

Affected Resources

System Process

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.

Nature	Type	ID	Name
MemberOf	Category - 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	Category - a CWE entry that contains a set of other entries that share a common characteristic.	847	The CERT Oracle Secure Coding Standard for Java (2011) Chapter 4 - Expressions (EXP)
MemberOf	Category - 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	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1001	SFP Secondary Cluster: Use of an Improper API
MemberOf	Category - 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	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1401	Comprehensive Categorization: Concurrency

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 Variant 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.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
CLASP			Unsafe function call from a signal handler
CERT C Secure Coding	SIG30-C	Exact	Call only asynchronous-safe functions within signal handlers
CERT C Secure Coding	SIG34-C		Do not call signal() from within interruptible signal handlers
The CERT Oracle Secure Coding Standard for Java (2011)	EXP01-J		Never dereference null pointers
Software Fault Patterns	SFP3		Use of an improper API

References

[REF-18]	Secure Software, Inc.. "The CLASP Application Security Process". 2005. <https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>. (URL validated: 2024-11-17)
[REF-62]	Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 13, "Signal Vulnerabilities", Page 791. 1st Edition. Addison Wesley. 2006.

Content History

Submissions
Submission Date	Submitter	Organization
2006-07-19 (CWE Draft 3, 2006-07-19)	CLASP
2006-07-19 (CWE Draft 3, 2006-07-19)
Modifications
Modification Date	Modifier	Organization
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 Detection_Factors, 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
2020-02-24	CWE Content Team	MITRE
2020-02-24	updated Description, References, Relationships
2019-01-03	CWE Content Team	MITRE
2019-01-03	updated Relationships, Taxonomy_Mappings
2017-11-08	CWE Content Team	MITRE
2017-11-08	updated Observed_Examples, Relationships, Taxonomy_Mappings
2014-07-30	CWE Content Team	MITRE
2014-07-30	updated Relationships, Taxonomy_Mappings
2012-10-30	CWE Content Team	MITRE
2012-10-30	updated Demonstrative_Examples
2012-05-11	CWE Content Team	MITRE
2012-05-11	updated References, Relationships, Taxonomy_Mappings
2011-09-13	CWE Content Team	MITRE
2011-09-13	updated Relationships, Taxonomy_Mappings
2011-06-27	CWE Content Team	MITRE
2011-06-27	updated Common_Consequences
2011-06-01	CWE Content Team	MITRE
2011-06-01	updated Common_Consequences, Relationships, Taxonomy_Mappings
2010-12-13	CWE Content Team	MITRE
2010-12-13	updated Demonstrative_Examples, Description, Name, Observed_Examples, Other_Notes, Potential_Mitigations, Relationships
2010-09-27	CWE Content Team	MITRE
2010-09-27	updated Relationships
2008-11-24	CWE Content Team	MITRE
2008-11-24	updated Relationships, Taxonomy_Mappings
2008-09-08	CWE Content Team	MITRE
2008-09-08	updated Applicable_Platforms, Common_Consequences, Description, Relationships, Other_Notes, Taxonomy_Mappings
2008-07-01	Eric Dalci	Cigital
2008-07-01	updated Time_of_Introduction
Previous Entry Names
Change Date	Previous Entry Name
2010-12-13	Unsafe Function Call from a Signal Handler


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Common Weakness Enumeration

CWE-479: Signal Handler Use of a Non-reentrant Function

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