CWE-456: Missing Initialization of a Variable

Definition

What is CWE-456?

This vulnerability occurs when a program uses a variable before giving it a starting value, causing the software to rely on unpredictable data left over in memory.

Missing initialization is a common coding mistake that can lead to crashes, incorrect calculations, or security bypasses. The risk is highest when the uninitialized variable controls security logic, like an authentication flag, or influences critical operations. Developers should proactively initialize all variables upon declaration, especially those used in security checks or before any conditional assignment. While SAST tools can detect this pattern, managing it across a large, evolving codebase is challenging. An ASPM platform like Plexicus uses AI to not only identify these flaws but also to suggest the precise code fix, automating remediation and saving significant manual review time.

Real-world impact

Real-world CVEs caused by CWE-456

CVE-2020-6078

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)
CVE-2019-3836

Chain: secure communications library does not initialize a local variable for a data structure (CWE-456), leading to access of an uninitialized pointer (CWE-824).
CVE-2018-14641

Chain: C union member is not initialized (CWE-456), leading to access of invalid pointer (CWE-824)
CVE-2009-2692

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).
CVE-2020-20739

A variable that has its value set in a conditional statement is sometimes used when the conditional fails, sometimes causing data leakage
CVE-2005-2978

Product uses uninitialized variables for size and index, leading to resultant buffer overflow.
CVE-2005-2109

Internal variable in PHP application is not initialized, allowing external modification.
CVE-2005-2193

Array variable not initialized in PHP application, leading to resultant SQL injection.

How attackers exploit it

Step-by-step attacker path

1
This function attempts to extract a pair of numbers from a user-supplied string.
2
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:
3
then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).
4
Here, an uninitialized field in a Java class is used in a seldom-called method, which would cause a NullPointerException to be thrown.
5
This code first authenticates a user, then allows a delete command if the user is an administrator.

Vulnerable code example

Vulnerable C

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

Vulnerable C

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 */* 
  		}

Attacker payload

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:

Attacker payload

123:

Secure code example

Secure Java

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.

Secure 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* 
  				...
  		}

What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.

Prevention checklist

How to prevent CWE-456

Implementation Ensure that critical variables are initialized before first use [REF-1485].
Requirements Choose a language that is not susceptible to these issues.

Detection signals

How to detect CWE-456

Automated Static Analysis High

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.)

CWE-456

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Frequently asked questions

What is CWE-456?

This vulnerability occurs when a program uses a variable before giving it a starting value, causing the software to rely on unpredictable data left over in memory.

How serious is CWE-456?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-456?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-456?

Ensure that critical variables are initialized before first use [REF-1485]. Choose a language that is not susceptible to these issues.

How does Plexicus detect and fix CWE-456?

Plexicus's SAST engine matches the data-flow signature for CWE-456 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-456?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/456.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-456

CWE-909 Parent

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Missing Initialization of a Variable

What is CWE-456?

Real-world CVEs caused by CWE-456

Step-by-step attacker path

Vulnerable C

Secure Java

How to prevent CWE-456

How to detect CWE-456

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-456

Missing Initialization of Resource

Uninitialized Value on Reset for Registers Holding Security Settings

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

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

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

Use of Uninitialized Variable

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`