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

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.

Primary

Implementation

Low

Integrity
Confidentiality
Availability
Execute Unauthorized Code or Commands
It may be possible to execute arbitrary code through the use of a write-what-where condition.

Integrity
Modify Memory
Modify Application Data
Signal race conditions often result in data corruption.

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.)
High

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.
Defense in Depth

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

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.

CVE-2005-0893
signal handler calls function that ultimately uses malloc()
https://www.cve.org/CVERecord?id=CVE-2005-0893

CVE-2004-2259
SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.
https://www.cve.org/CVERecord?id=CVE-2004-2259

System Process

Unsafe function call from a signal handler

SIG30-C
Call only asynchronous-safe functions within signal handlers
Exact

SIG34-C
Do not call signal() from within interruptible signal handlers

EXP01-J
Never dereference null pointers

SFP3
Use of an improper API

Allowed
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.
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.

CLASP
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Applicable_Platforms, Common_Consequences, Description, Relationships, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2008-11-24
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2010-09-27
updated Relationships

CWE Content Team
MITRE
2010-12-13
updated Demonstrative_Examples, Description, Name, Observed_Examples, Other_Notes, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences

CWE Content Team
MITRE
2011-09-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-10-30
updated Demonstrative_Examples

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2017-11-08
updated Observed_Examples, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2020-02-24
updated Description, References, Relationships

CWE Content Team
MITRE
2020-12-10
updated Common_Consequences

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Demonstrative_Examples

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Demonstrative_Examples

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Weakness_Ordinalities

Unsafe Function Call from a Signal Handler