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 Variant Draft
Missing Initialization of a Variable
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.
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
-
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: secure communications library does not initialize a local variable for a data structure (CWE-456), leading to access of an uninitialized pointer (CWE-824).
-
Chain: C union member is not initialized (CWE-456), leading to access of invalid pointer (CWE-824)
-
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.
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.
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:
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.
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
Plexicus auto-detects CWE-456 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-456?
How serious is CWE-456?
What languages or platforms are affected by CWE-456?
How can I prevent CWE-456?
How does Plexicus detect and fix CWE-456?
Where can I learn more about CWE-456?
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
Missing Initialization of Resource
The software fails to properly set up a critical resource before using it.
CWE-1271 Sibling
Uninitialized Value on Reset for Registers Holding Security Settings
Security-critical hardware registers start with random, unpredictable values when a device powers on or resets, creating an immediate…
CWE-89 Can precede
Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')
SQL Injection occurs when an application builds a database query using untrusted user input without properly sanitizing it. This allows an…
CWE-120 Can precede
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
This vulnerability occurs when a program copies data from one memory location to another without first verifying that the source data will…
CWE-98 Can precede
Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion')
This vulnerability occurs when a PHP application uses unvalidated or insufficiently restricted user input directly within file inclusion…
CWE-457 Can precede
Use of Uninitialized Variable
This vulnerability occurs when a program accesses a variable before it has been assigned a value, leading to unpredictable behavior and…
Resources
Further reading
- MITRE — official CWE-456 https://cwe.mitre.org/data/definitions/456.html
- Automated Source Code Reliability Measure (ASCRM) http://www.omg.org/spec/ASCRM/1.0/
- Automated Source Code Security Measure (ASCSM) http://www.omg.org/spec/ASCSM/1.0/
- uninitialized variable vulnerability - Problem with boolean variables that are forcibly initialized to false by the Java compiler https://github.com/windshock/uninitialized-variable-vulnerability/blob/main/README.md
- The Java Language Specification, Java SE 7 Edition https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.12.5
- D3FEND: D3-VI Variable Initialization https://d3fend.mitre.org/technique/d3f:VariableInitialization/
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