The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.
This can have security implications when the associated resource is expected to have certain properties or values, such as a variable that determines whether a user has been authenticated or not.

Primary

Resultant

Implementation
This weakness can occur in code paths that are not well-tested, such as rare error conditions. This is because the use of uninitialized data would be noticed as a bug during frequently-used functionality.

Operation

Medium

Confidentiality
Read Memory
Read Application Data
When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.

Access Control
Bypass Protection Mechanism
If security-critical decisions rely on a variable having a "0" or equivalent value, and the programming language performs this initialization on behalf of the programmer, then a bypass of security may occur.

Availability
DoS: Crash, Exit, or Restart
The uninitialized data may contain values that cause program flow to change in ways that the programmer did not intend. For example, if an uninitialized variable is used as an array index in C, then its previous contents may produce an index that is outside the range of the array, possibly causing a crash or an exit in other environments.

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
Initialization problems may be detected with a stress-test by calling the software simultaneously from a large number of threads or processes, and look for evidence of any unexpected behavior. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Moderate

Manual Dynamic Analysis
Identify error conditions that are not likely to occur during normal usage and trigger them. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. Monitor the software for any unexpected behavior. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself.

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.)
High

Requirements
Language Selection

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
For example, in Java, if the programmer does not explicitly initialize a variable, then the code could produce a compile-time error (if the variable is local) or automatically initialize the variable to the default value for the variable's type. In Perl, if explicit initialization is not performed, then a default value of undef is assigned, which is interpreted as 0, false, or an equivalent value depending on the context in which the variable is accessed.

Architecture and Design
Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.

Implementation
Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage.

Implementation
Pay close attention to complex conditionals that affect initialization, since some conditions might not perform the initialization.

Implementation
Avoid race conditions (CWE-362) during initialization routines.

Build and Compilation
Run or compile your product with settings that generate warnings about uninitialized variables or data.

Testing
Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.

Here, a boolean initiailized field is consulted to ensure that initialization tasks are only completed once. However, the field is mistakenly set to true during static initialization, so the initialization code is never reached.

private boolean initialized = true;public void someMethod() {
if (!initialized) {

// perform initialization tasks
...
initialized = true;
}

The following code intends to limit certain operations to the administrator only.

$username = GetCurrentUser();$state = GetStateData($username);if (defined($state)) {$uid = ExtractUserID($state);}

# do stuff
if ($uid == 0) {DoAdminThings();}

If the application is unable to extract the state information - say, due to a database timeout - then the $uid variable will not be explicitly set by the programmer. This will cause $uid to be regarded as equivalent to "0" in the conditional, allowing the original user to perform administrator actions. Even if the attacker cannot directly influence the state data, unexpected errors could cause incorrect privileges to be assigned to a user just by accident.

The following code intends to concatenate a string to a variable and print the string.

char str[20];strcat(str, "hello world");printf("%s", str);

This might seem innocent enough, but str was not initialized, so it contains random memory. As a result, str[0] might not contain the null terminator, so the copy might start at an offset other than 0. The consequences can vary, depending on the underlying memory.
If a null terminator is found before str[8], then some bytes of random garbage will be printed before the "hello world" string. The memory might contain sensitive information from previous uses, such as a password (which might occur as a result of CWE-14 or CWE-244). In this example, it might not be a big deal, but consider what could happen if large amounts of memory are printed out before the null terminator is found.
If a null terminator isn't found before str[8], then a buffer overflow could occur, since strcat will first look for the null terminator, then copy 12 bytes starting with that location. Alternately, a buffer over-read might occur (CWE-126) if a null terminator isn't found before the end of the memory segment is reached, leading to a segmentation fault and crash.

CVE-2001-1471
chain: an invalid value prevents a library file from being included, skipping initialization of key variables, leading to resultant eval injection.
https://www.cve.org/CVERecord?id=CVE-2001-1471

CVE-2008-3637
Improper error checking in protection mechanism produces an uninitialized variable, allowing security bypass and code execution.
https://www.cve.org/CVERecord?id=CVE-2008-3637

CVE-2008-4197
Use of uninitialized memory may allow code execution.
https://www.cve.org/CVERecord?id=CVE-2008-4197

CVE-2008-2934
Free of an uninitialized pointer leads to crash and possible code execution.
https://www.cve.org/CVERecord?id=CVE-2008-2934

CVE-2007-3749
OS kernel does not reset a port when starting a setuid program, allowing local users to access the port and gain privileges.
https://www.cve.org/CVERecord?id=CVE-2007-3749

CVE-2008-0063
Product does not clear memory contents when generating an error message, leading to information leak.
https://www.cve.org/CVERecord?id=CVE-2008-0063

CVE-2008-0062
Lack of initialization triggers NULL pointer dereference or double-free.
https://www.cve.org/CVERecord?id=CVE-2008-0062

CVE-2008-0081
Uninitialized variable leads to code execution in popular desktop application.
https://www.cve.org/CVERecord?id=CVE-2008-0081

CVE-2008-3688
chain: Uninitialized variable leads to infinite loop.
https://www.cve.org/CVERecord?id=CVE-2008-3688

CVE-2008-3475
chain: Improper initialization leads to memory corruption.
https://www.cve.org/CVERecord?id=CVE-2008-3475

CVE-2008-5021
Composite: race condition allows attacker to modify an object while it is still being initialized, causing software to access uninitialized memory.
https://www.cve.org/CVERecord?id=CVE-2008-5021

CVE-2005-1036
Chain: Bypass of access restrictions due to improper authorization (CWE-862) of a user results from an improperly initialized (CWE-909) I/O permission bitmap
https://www.cve.org/CVERecord?id=CVE-2005-1036

CVE-2008-3597
chain: game server can access player data structures before initialization has happened leading to NULL dereference
https://www.cve.org/CVERecord?id=CVE-2008-3597

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)
https://www.cve.org/CVERecord?id=CVE-2009-2692

CVE-2009-0949
chain: improper initialization of memory can lead to NULL dereference
https://www.cve.org/CVERecord?id=CVE-2009-0949

CVE-2009-3620
chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference
https://www.cve.org/CVERecord?id=CVE-2009-3620

Incorrect initialization

ARR02-C
Explicitly specify array bounds, even if implicitly defined by an initializer

DCL00-J
Prevent class initialization cycles

SFP4
Unchecked Status Condition

Discouraged
This CWE entry is a level-1 Class (i.e., a child of a Pillar). It might have lower-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

PLOVER
2008-04-11
Draft 9
2008-04-11

Sean Eidemiller
Cigital
2008-07-01
added/updated demonstrative examples

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2008-11-24
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2009-01-12
updated Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Modes_of_Introduction, Name, Observed_Examples, Potential_Mitigations, References, Relationships, Weakness_Ordinalities

CWE Content Team
MITRE
2009-03-10
updated Potential_Mitigations

CWE Content Team
MITRE
2009-05-27
updated Description, Relationships

CWE Content Team
MITRE
2009-07-27
updated Related_Attack_Patterns

CWE Content Team
MITRE
2009-10-29
updated Common_Consequences

CWE Content Team
MITRE
2010-02-16
updated Potential_Mitigations

CWE Content Team
MITRE
2010-04-05
updated Applicable_Platforms

CWE Content Team
MITRE
2010-06-21
updated Detection_Factors, Potential_Mitigations

CWE Content Team
MITRE
2010-09-27
updated Observed_Examples

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2011-09-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2013-02-21
updated Demonstrative_Examples, Relationships

CWE Content Team
MITRE
2014-07-30
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-01-19
updated Type

CWE Content Team
MITRE
2017-11-08
updated References, Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Related_Attack_Patterns, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-06-20
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2020-06-25
updated Relationships

CWE Content Team
MITRE
2020-08-20
updated Relationships

CWE Content Team
MITRE
2020-12-10
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Observed_Examples

CWE Content Team
MITRE
2023-01-31
updated Description, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, References, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Relationships

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-09-09
4.18
2025-09-09
updated References, Relationships

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Observed_Examples

Incorrect or Incomplete Initialization