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Common Weakness Enumeration

A community-developed list of SW & HW weaknesses that can become vulnerabilities

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Home > CWE List > CWE-456: Missing Initialization of a Variable (4.16)  
ID

CWE-456: Missing Initialization of a Variable

Weakness ID: 456
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 does not initialize critical variables, which causes the execution environment to use unexpected values.
+ Common Consequences
Section HelpThis 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.
Scope Impact Likelihood
Integrity
Other

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.
+ Potential Mitigations

Phase: Implementation

Check that critical variables are initialized.

Phase: Testing

Use a static analysis tool to spot non-initialized variables.
+ Relationships
Section Help 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" (CWE-1000)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 909 Missing Initialization of Resource
CanPrecede Base 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. 89 Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')
CanPrecede 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. 98 Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion')
CanPrecede Base 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. 120 Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CanPrecede 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. 457 Use of Uninitialized Variable
Section Help 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 "CISQ Quality Measures (2020)" (CWE-1305)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 665 Improper Initialization
Section Help 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 "CISQ Data Protection Measures" (CWE-1340)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 665 Improper Initialization
+ Modes Of Introduction
Section HelpThe 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
Section HelpThis 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

Class: Not Language-Specific (Undetermined Prevalence)

+ Demonstrative Examples

Example 1

This function attempts to extract a pair of numbers from a user-supplied string.

(bad code)
Example Language:
void parse_data(char *untrusted_input){
int m, n, error;
error = sscanf(untrusted_input, "%d:%d", &m, &n);
if ( EOF == error ){
die("Did not specify integer value. Die evil hacker!\n");
}
/* proceed assuming n and m are initialized correctly */
}

This code attempts to extract two integer values out of a formatted, user-supplied input. However, if an attacker were to provide an input of the form:

(attack code)
 
123:

then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).


Example 2

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

(bad code)
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 3

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

(bad code)
Example Language: PHP 
if (authenticate($username,$password) && setAdmin($username)){
$isAdmin = true;
}
/.../

if ($isAdmin){
deleteUser($userToDelete);
}

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 4

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.

(bad 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() {
...
}

// 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.

(good 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
...

}

Example 5

This example will leave test_string in an unknown condition when i is the same value as err_val, because test_string is not initialized (CWE-456). Depending on where this code segment appears (e.g. within a function body), test_string might be random if it is stored on the heap or stack. If the variable is declared in static memory, it might be zero or NULL. Compiler optimization might contribute to the unpredictability of this address.

(bad code)
Example Language:
char *test_string;
if (i != err_val)
{
test_string = "Hello World!";
}
printf("%s", test_string);

When the printf() is reached, test_string might be an unexpected address, so the printf might print junk strings (CWE-457).

To fix this code, there are a couple approaches to making sure that test_string has been properly set once it reaches the printf().

One solution would be to set test_string to an acceptable default before the conditional:

(good code)
Example Language:
char *test_string = "Done at the beginning";
if (i != err_val)
{
test_string = "Hello World!";
}
printf("%s", test_string);

Another solution is to ensure that each branch of the conditional - including the default/else branch - could ensure that test_string is set:

(good code)
Example Language:
char *test_string;
if (i != err_val)
{
test_string = "Hello World!";
}
else {
test_string = "Done on the other side!";
}
printf("%s", test_string);

+ Observed Examples
Reference Description
Chain: The return value of a function returning a pointer is not checked for success (CWE-252) resulting in the later use of an uninitialized variable (CWE-456) and a null pointer dereference (CWE-476)
Chain: Use of an unimplemented network socket operation pointing to an uninitialized handler function (CWE-456) causes a crash because of a null pointer dereference (CWE-476).
A variable that has its value set in a conditional statement is sometimes used when the conditional fails, sometimes causing data leakage
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.
+ Detection Methods

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

+ Memberships
Section HelpThis 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 CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 808 2010 Top 25 - Weaknesses On the Cusp
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 867 2011 Top 25 - Weaknesses On the Cusp
MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 884 CWE Cross-section
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 998 SFP Secondary Cluster: Glitch in Computation
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1129 CISQ Quality Measures (2016) - Reliability
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1131 CISQ Quality Measures (2016) - Security
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1167 SEI CERT C Coding Standard - Guidelines 12. Error Handling (ERR)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1180 SEI CERT Perl Coding Standard - Guidelines 02. Declarations and Initialization (DCL)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1416 Comprehensive Categorization: Resource Lifecycle Management
+ 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.
+ Notes

Relationship

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 Name Node ID Fit Mapped Node Name
PLOVER Missing Initialization
Software Fault Patterns SFP1 Glitch in computation
CERT C Secure Coding ERR30-C CWE More Abstract Set errno to zero before calling a library function known to set errno, and check errno only after the function returns a value indicating failure
SEI CERT Perl Coding Standard DCL04-PL Exact Always initialize local variables
SEI CERT Perl Coding Standard DCL33-PL Imprecise Declare identifiers before using them
OMG ASCSM ASCSM-CWE-456
OMG ASCRM ASCRM-CWE-456
+ 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.
[REF-961] Object Management Group (OMG). "Automated Source Code Reliability Measure (ASCRM)". ASCRM-CWE-456. 2016-01. <http://www.omg.org/spec/ASCRM/1.0/>.
[REF-962] Object Management Group (OMG). "Automated Source Code Security Measure (ASCSM)". ASCSM-CWE-456. 2016-01. <http://www.omg.org/spec/ASCSM/1.0/>.
+ Content History
+ Submissions
Submission Date Submitter Organization
2006-07-19
(CWE Draft 3, 2006-07-19)
PLOVER
+ Modifications
Modification Date Modifier Organization
2008-07-01 Sean Eidemiller Cigital
added/updated demonstrative examples
2008-07-01 Eric Dalci Cigital
updated Potential_Mitigations, Time_of_Introduction
2008-09-08 CWE Content Team MITRE
updated Relationships, Other_Notes, Taxonomy_Mappings
2010-02-16 CWE Content Team MITRE
updated Relationships
2010-04-05 CWE Content Team MITRE
updated Applicable_Platforms, Demonstrative_Examples
2010-06-21 CWE Content Team MITRE
updated Other_Notes, Relationship_Notes
2011-03-29 CWE Content Team MITRE
updated Demonstrative_Examples
2011-06-01 CWE Content Team MITRE
updated Common_Consequences
2011-06-27 CWE Content Team MITRE
updated Common_Consequences, Relationships
2012-05-11 CWE Content Team MITRE
updated References, Relationships
2012-10-30 CWE Content Team MITRE
updated Potential_Mitigations
2013-02-21 CWE Content Team MITRE
updated Name, Relationships
2014-07-30 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2017-11-08 CWE Content Team MITRE
updated Taxonomy_Mappings
2019-01-03 CWE Content Team MITRE
updated References, Relationships, Taxonomy_Mappings
2019-06-20 CWE Content Team MITRE
updated Relationships, Type
2020-02-24 CWE Content Team MITRE
updated Relationships
2020-06-25 CWE Content Team MITRE
updated Demonstrative_Examples
2020-08-20 CWE Content Team MITRE
updated Relationships
2020-12-10 CWE Content Team MITRE
updated Relationships
2021-03-15 CWE Content Team MITRE
updated Demonstrative_Examples, Observed_Examples, Relationships
2023-01-31 CWE Content Team MITRE
updated Description
2023-04-27 CWE Content Team MITRE
updated Detection_Factors, Relationships
2023-06-29 CWE Content Team MITRE
updated Mapping_Notes
+ Previous Entry Names
Change Date Previous Entry Name
2013-02-21 Missing Initialization
Page Last Updated: November 19, 2024