The product does not initialize a critical resource.
Many resources require initialization before they can be properly used. If a resource is not initialized, it could contain unpredictable or expired data, or it could be initialized to defaults that are invalid. This can have security implications when the resource is expected to have certain properties or values.

Primary

Resultant

Implementation

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.

Availability
DoS: Crash, Exit, or Restart
The uninitialized resource may contain values that cause program flow to change in ways that the programmer did not intend.

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

Implementation
Explicitly initialize the resource before use. If this is performed through an API function or standard procedure, follow all specified steps.

Implementation
Pay close attention to complex conditionals that affect initialization, since some branches 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.

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.

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
(CWE-456). 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.

char *test_string;
if (i != err_val)
{
test_string = "Hello World!";
}
printf("%s", test_string);

When the printf() is reached,
test_string might be an unexpected address, so the
printf might print junk strings (CWE-457).

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:

char *test_string = "Done at the beginning";
if (i != err_val)
{
test_string = "Hello World!";
}
printf("%s", test_string);

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

char *test_string;
if (i != err_val)
{
test_string = "Hello World!";
}
else {
test_string = "Done on the other side!";
}
printf("%s", test_string);

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
https://www.cve.org/CVERecord?id=CVE-2020-20739

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

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

CWE Content Team
MITRE
2012-12-21
2.4
2013-02-21
New weakness based on discussion on the CWE research list in December 2012.

CWE Content Team
MITRE
2019-06-20
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples, Observed_Examples

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

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Mapping_Notes, Type

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