CWE-476: NULL Pointer Dereference

CWE Top 25 #13One of MITRE's most dangerous software weaknesses. Read our plain-English guide to NULL Pointer Dereference.

Description

The product dereferences a pointer that it expects to be valid but is NULL.

Abstraction: BaseA weakness specific enough to point to detection and prevention methods.
Likelihood of exploit: Medium
Status: Stable

Common consequences

Availability
DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
IntegrityConfidentiality
Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.

Potential mitigations

Implementation
For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
Requirements
Select a programming language that is not susceptible to these issues.
ImplementationEffectiveness: Moderate
Check the results of all functions that return a value and verify that the value is non-null before acting upon it.
Architecture and Design
Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.
Implementation
Explicitly initialize all variables and other data stores, either during declaration or just before the first usage.

Related weaknesses

Parent weaknesses

CAPEC attack patterns that exploit it

CWE 4.20 links no CAPEC attack pattern to this weakness.

Common consequences

Availability

DoS: Crash, Exit, or Restart

NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.

IntegrityConfidentiality

Execute Unauthorized Code or Commands; Read Memory; Modify Memory

In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.

Potential mitigations

Implementation

For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.

Requirements

Select a programming language that is not susceptible to these issues.

ImplementationEffectiveness: Moderate

Check the results of all functions that return a value and verify that the value is non-null before acting upon it.

Architecture and Design

Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.

Implementation

Explicitly initialize all variables and other data stores, either during declaration or just before the first usage.