Common Weakness Enumeration

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CWE-456: Missing Initialization of a Variable

Weakness ID: 456
Abstraction: Base
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The software does not initialize critical variables, which causes the execution environment to use unexpected values.
+ Relationships

The table(s) below 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 "Development Concepts" (CWE-699)
MemberOfCategoryCategory452Initialization and Cleanup Errors
CanPrecedeVariantVariant457Use of Uninitialized Variable
+ 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 software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

+ Applicable Platforms
The listings below show 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.


(Language-Independent classes): (Undetermined Prevalence)

+ Common Consequences

The table below 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.


Technical Impact: Unexpected State; Quality Degradation; Varies by Context

The uninitialized data may be invalid, causing logic errors within the program. In some cases, this could result in a security problem.
+ Demonstrative Examples

Example 1

Here, an uninitialized field in a Java class is used in a seldom-called method, which would cause a NullPointerException to be thrown.

Example Language: Java 
private User user;
public void someMethod() {
// Do something interesting.
// Throws NPE if user hasn't been properly initialized.

String username = user.getName();


Example 2

This code first authenticates a user, then allows a delete command if the user is an administrator.

Example Language: PHP 
if (authenticate($username,$password) && setAdmin($username)){
$isAdmin = true;


if ($isAdmin){


The $isAdmin variable is set to true if the user is an admin, but is uninitialized otherwise. If PHP's register_globals feature is enabled, an attacker can set uninitialized variables like $isAdmin to arbitrary values, in this case gaining administrator privileges by setting $isAdmin to true.

Example 3

In the following Java code the BankManager class uses the user variable of the class User to allow authorized users to perform bank manager tasks. The user variable is initialized within the method setUser that retrieves the User from the User database. The user is then authenticated as unauthorized user through the method authenticateUser.

Example Language: Java 
public class BankManager {
// user allowed to perform bank manager tasks
private User user = null;
private boolean isUserAuthentic = false;
// constructor for BankManager class

public BankManager() {

// retrieve user from database of users

public User getUserFromUserDatabase(String username){

// set user variable using username

public void setUser(String username) {
this.user = getUserFromUserDatabase(username);

// authenticate user

public boolean authenticateUser(String username, String password) {
if (username.equals(user.getUsername()) && password.equals(user.getPassword())) {
isUserAuthentic = true;

return isUserAuthentic;

// methods for performing bank manager tasks



However, if the method setUser is not called before authenticateUser then the user variable will not have been initialized and will result in a NullPointerException. The code should verify that the user variable has been initialized before it is used, as in the following code.

Example Language: Java 
public class BankManager {
// user allowed to perform bank manager tasks
private User user = null;
private boolean isUserAuthentic = false;
// constructor for BankManager class

public BankManager(String username) {
user = getUserFromUserDatabase(username);

// retrieve user from database of users

public User getUserFromUserDatabase(String username) {...}
// authenticate user

public boolean authenticateUser(String username, String password) {
if (user == null) {
System.out.println("Cannot find user " + username);

else {
if (password.equals(user.getPassword())) {
isUserAuthentic = true;


return isUserAuthentic;

// methods for performing bank manager tasks

+ Observed Examples
Product uses uninitialized variables for size and index, leading to resultant buffer overflow.
Internal variable in PHP application is not initialized, allowing external modification.
Array variable not initialized in PHP application, leading to resultant SQL injection.
+ Potential Mitigations

Phase: Implementation

Check that critical variables are initialized.

Phase: Testing

Use a static analysis tool to spot non-initialized variables.
+ 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.
+ Notes


This weakness is a major factor in a number of resultant weaknesses, especially in web applications that allow global variable initialization (such as PHP) with libraries that can be directly requested.

Research Gap

It is highly likely that a large number of resultant weaknesses have missing initialization as a primary factor, but researcher reports generally do not provide this level of detail.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERMissing Initialization
Software Fault PatternsSFP1Glitch in computation
CERT C Secure CodingERR30-CCWE More AbstractSet errno to zero before calling a library function known to set errno, and check errno only after the function returns a value indicating failure
CERT Perl Secure CodingDCL04-PLExactAlways initialize local variables
CERT Perl Secure CodingDCL33-PLImpreciseDeclare identifiers before using them
+ References
[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 7, "Variable Initialization", Page 312.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submission DateSubmitterOrganizationSource
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigital
added/updated demonstrative examples
2008-07-01Eric DalciCigital
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Relationships, Other_Notes, Taxonomy_Mappings
2010-02-16CWE Content TeamMITRE
updated Relationships
2010-04-05CWE Content TeamMITRE
updated Applicable_Platforms, Demonstrative_Examples
2010-06-21CWE Content TeamMITRE
updated Other_Notes, Relationship_Notes
2011-03-29CWE Content TeamMITRE
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2011-06-27CWE Content TeamMITRE
updated Common_Consequences, Relationships
2012-05-11CWE Content TeamMITRE
updated References, Relationships
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2013-02-21CWE Content TeamMITRE
updated Name, Relationships
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2013-02-21Missing Initialization

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Page Last Updated: November 14, 2017