Missing Initialization of a Variable

Draft Variant

Structure: Simple

Description

The product does not initialize critical variables, which causes the execution environment to use unexpected values.

Common Consequences 1

Scope: IntegrityOther

Impact: Unexpected StateQuality DegradationVaries by Context

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

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 2

Phase: Implementation

Strategy: Attack Surface Reduction

Ensure that critical variables are initialized before first use [REF-1485].

Phase: Requirements

Strategy: Language Selection

Choose a language that is not susceptible to these issues.

Demonstrative Examples 6

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

Code Example:

Bad

/* 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:

Code Example:Attack
bash

then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (Use of Uninitialized Variable).

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

Code Example:

Bad

Java

java

// Do something interesting.* ...

java

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

Code Example:

Bad

PHP

php

/.../*

php

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.

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.

Code Example:

Bad

Java

java

// user allowed to perform bank manager tasks* private User user = null; private boolean isUserAuthentic = false;

java

java

// set user variable using username* public void setUser(String username) { ``` this.user = getUserFromUserDatabase(username); }

java

// 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.

Code Example:

Good

Java

java

// user allowed to perform bank manager tasks* private User user = null; private boolean isUserAuthentic = false;

java

java

// methods for performing bank manager tasks* ... }

ID : DX-144

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 (Missing Initialization of a Variable). 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.

Code Example:

Bad

char *test_string; if (i != err_val) {

When the printf() is reached, test_string might be an unexpected address, so the printf might print junk strings (Use of Uninitialized Variable). 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:

Code Example:

Good

char *test_string = "Done at the beginning"; if (i != err_val) {

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

Code Example:

Good

char *test_string; if (i != err_val) {

Consider the following merchant server application as implemented in [REF-1475]. It receives card payment information (orderPgData instance in OrderPgData.java) from the payment gateway (such as PayPal). The next step is to complete the payment (finalizeOrder() in Main.java). The merchant server validates the amount (validateAmount() in OrderPgData.java), and if the validation is successful, then the payment is completed.

Code Example:

Bad

Java

File: OrderPgData.java

public class OrderPgData {

java

Code Example:

Bad

Java

File: PgServiceResolver.java

public class PgServiceResolver {

java

Code Example:

Bad

Java

File: Main.java

public class Main {

java

In PgServiceResolver.java, when pgType is "card" indicating a card payment, orderPgData.validateAmount() is not called - that is, the amount is not validated to be the same as the expected price. Since isPaymentAmountTampered is declared as a private boolean, but it is not initialized, it is forcibly initialized to false by the Java compiler [REF-1476]. If the adversary modifies the price, e.g., changing paymentAmount from 100 to 10, then no validation is performed. Since isPaymentAmountTampered is "false" because of the default initialization, the code finishes processing the payment because it does not believe that the amount has been changed.

This weakness could be addressed by setting the value of isPaymentAmountTampered to true. This is a "secure-by-default" value that reflects a "default deny" policy - i.e., it's assumed that the payment amount is tampered, and only a special validation step can change this assumption.

Code Example:

Good

Java

File: OrderPgData.java ...

java

Observed Examples 8

CVE-2020-6078Chain: The return value of a function returning a pointer is not checked for success (Unchecked Return Value) resulting in the later use of an uninitialized variable (Missing Initialization of a Variable) and a null pointer dereference (NULL Pointer Dereference)

CVE-2019-3836Chain: secure communications library does not initialize a local variable for a data structure (Missing Initialization of a Variable), leading to access of an uninitialized pointer (Access of Uninitialized Pointer).

CVE-2018-14641Chain: C union member is not initialized (Missing Initialization of a Variable), leading to access of invalid pointer (Access of Uninitialized Pointer)

CVE-2009-2692Chain: Use of an unimplemented network socket operation pointing to an uninitialized handler function (Missing Initialization of a Variable) causes a crash because of a null pointer dereference (NULL Pointer Dereference).

CVE-2020-20739A variable that has its value set in a conditional statement is sometimes used when the conditional fails, sometimes causing data leakage

CVE-2005-2978Product uses uninitialized variables for size and index, leading to resultant buffer overflow.

CVE-2005-2109Internal variable in PHP application is not initialized, allowing external modification.

CVE-2005-2193Array variable not initialized in PHP application, leading to resultant SQL injection.

References 6

The Art of Software Security Assessment

Mark Dowd, John McDonald, and Justin Schuh

Addison Wesley

2006

ID: REF-62

Automated Source Code Reliability Measure (ASCRM)

Object Management Group (OMG)

01-2016

http://www.omg.org/spec/ASCRM/1.0/

ID: REF-961

Automated Source Code Security Measure (ASCSM)

Object Management Group (OMG)

01-2016

http://www.omg.org/spec/ASCSM/1.0/

ID: REF-962

uninitialized variable vulnerability - Problem with boolean variables that are forcibly initialized to false by the Java compiler

windshock

13-09-2022

https://github.com/windshock/uninitialized-variable-vulnerability/blob/main/README.md(2025-04-02)

ID: REF-1475

The Java Language Specification, Java SE 7 Edition

James Gosling, Bill Joy, Guy Steele, Gilad Bracha, and Alex Buckley

28-02-2013

https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.12.5(2025-04-02)

ID: REF-1476

D3FEND: D3-VI Variable Initialization

D3FEND

https://d3fend.mitre.org/technique/d3f:VariableInitialization/(2025-09-08)

ID: REF-1485

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Missing Initialization of Resource (CWE-909)

ChildOf:

Improper Initialization (CWE-665)

ChildOf:

Improper Initialization (CWE-665)

CanPrecede:

Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection') (CWE-89)

CanPrecede:

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') (CWE-120)

CanPrecede:

Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion') (CWE-98)

CanPrecede:

Use of Uninitialized Variable (CWE-457)

Taxonomy Mapping

PLOVER
Software Fault Patterns
CERT C Secure Coding
SEI CERT Perl Coding Standard
SEI CERT Perl Coding Standard
OMG ASCSM
OMG ASCRM

Notes

RelationshipThis 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 GapIt 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.