Signal Handler Use of a Non-reentrant Function

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 2

Scope: IntegrityConfidentialityAvailability

Impact: Execute Unauthorized Code or Commands

It may be possible to execute arbitrary code through the use of a write-what-where condition.

Scope: Integrity

Impact: Modify MemoryModify Application Data

Signal race conditions often result in data corruption.

Detection Methods 1

Automated Static AnalysisHigh

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.)

Potential Mitigations 4

Phase: Requirements

Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness.

Phase: Architecture and Design

Design signal handlers to only set flags rather than perform complex functionality.

Phase: Implementation

Ensure that non-reentrant functions are not found in signal handlers.

Phase: 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

Demonstrative Examples 1

ID : DX-171

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

Code Example:Bad
C
c

Observed Examples 2

CVE-2005-0893signal handler calls function that ultimately uses malloc()

CVE-2004-2259SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.

References 2

The CLASP Application Security Process

Secure Software, Inc.

2005

https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf(2024-11-17)

ID: REF-18

The Art of Software Security Assessment

Mark Dowd, John McDonald, and Justin Schuh

Addison Wesley

2006

ID: REF-62

Likelihood of Exploit

Low

Applicable Platforms

Languages:

C : UndeterminedC++ : Undetermined

Modes of Introduction

Implementation

Affected Resources

System Process

Related Weaknesses

ChildOf:

Signal Handler with Functionality that is not Asynchronous-Safe (CWE-828)

ChildOf:

Use of a Non-reentrant Function in a Concurrent Context (CWE-663)

CanPrecede:

Write-what-where Condition (CWE-123)

Taxonomy Mapping

CLASP
CERT C Secure Coding
CERT C Secure Coding
The CERT Oracle Secure Coding Standard for Java (2011)
Software Fault Patterns