Description
The product does not initialize critical variables, which causes the execution environment to use unexpected values.
Potential Impact
Integrity, Other
Unexpected State, Quality Degradation, Varies by Context
Demonstrative Examples
This function attempts to extract a pair of numbers from a user-supplied string.
Bad
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
123:then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).
Here, an uninitialized field in a Java class is used in a seldom-called method, which would cause a NullPointerException to be thrown.
Bad
private User user;public void someMethod() {
// Do something interesting.
...
// Throws NPE if user hasn't been properly initialized.
String username = user.getName();
}This code first authenticates a user, then allows a delete command if the user is an administrator.
Bad
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.
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
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
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
...
}Mitigations & Prevention
Ensure that critical variables are initialized before first use [REF-1485].
Choose a language that is not susceptible to these issues.
Detection Methods
- 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 sea
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| 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. |
Related Weaknesses
Taxonomy Mappings
- PLOVER: — Missing Initialization
- Software Fault Patterns: SFP1 — Glitch in computation
- CERT C Secure Coding: ERR30-C — 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 — Always initialize local variables
- SEI CERT Perl Coding Standard: DCL33-PL — Declare identifiers before using them
- OMG ASCSM: ASCSM-CWE-456 —
- OMG ASCRM: ASCRM-CWE-456 —
Frequently Asked Questions
What is CWE-456?
CWE-456 (Missing Initialization of a Variable) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product does not initialize critical variables, which causes the execution environment to use unexpected values.
How can CWE-456 be exploited?
Attackers can exploit CWE-456 (Missing Initialization of a Variable) to unexpected state, quality degradation, varies by context. This weakness is typically introduced during the Implementation phase of software development.
How do I prevent CWE-456?
Key mitigations include: Ensure that critical variables are initialized before first use [REF-1485].
What is the severity of CWE-456?
CWE-456 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 8 real-world CVEs.