Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE Top 25 Most Dangerous Software Errors
Home > CWE List > CWE- Individual Dictionary Definition (3.4.1)  

CWE-908: Use of Uninitialized Resource

Weakness ID: 908
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software uses a resource that has not been properly initialized.
+ Extended Description
This can have security implications when the associated resource is expected to have certain properties or values.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More general than a Base weakness.664Improper Control of a Resource Through its Lifetime
CanFollowBaseBase - a weakness that is described in an abstract fashion, but with sufficient details to infer specific methods for detection and prevention. More general than a Variant weakness, but more specific than a Class weakness.909Missing Initialization of Resource
+ Relevant to the view "Development Concepts" (CWE-699)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.452Initialization and Cleanup Errors
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.


Technical Impact: 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.

Technical Impact: 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.
+ Likelihood Of Exploit
+ Demonstrative Examples

Example 1

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.

(bad code)
Example Language: Java 
private boolean initialized = true;
public void someMethod() {
if (!initialized) {

// perform initialization tasks

initialized = true;

Example 2

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

(bad code)
Example Language: Perl 
$username = GetCurrentUser();
$state = GetStateData($username);
if (defined($state)) {
$uid = ExtractUserID($state);

# do stuff
if ($uid == 0) {

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.

Example 3

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

(bad code)
Example Language:
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.

+ Observed Examples
Use of uninitialized memory may allow code execution.
Free of an uninitialized pointer leads to crash and possible code execution.
Product does not clear memory contents when generating an error message, leading to information leak.
Lack of initialization triggers NULL pointer dereference or double-free.
Uninitialized variable leads to code execution in popular desktop application.
chain: Uninitialized variable leads to infinite loop.
chain: Improper initialization leads to memory corruption.
Permission bitmap is not properly initialized, leading to resultant privilege elevation or DoS.
chain: game server can access player data structures before initialization has happened leading to NULL dereference
chain: uninitialized function pointers can be dereferenced allowing code execution
chain: improper initialization of memory can lead to NULL dereference
chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference
+ Potential Mitigations

Phase: Implementation

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

Phase: Implementation

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

Phase: Implementation

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

Phase: Build and Compilation

Run or compile the software with settings that generate warnings about uninitialized variables or data.
+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
(where the weakness is typically related to the presence of some other weaknesses)
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1157SEI CERT C Coding Standard - Guidelines 03. Expressions (EXP)
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CERT C Secure CodingEXP33-CCWE More AbstractDo not read uninitialized memory
+ References
[REF-436] mercy. "Exploiting Uninitialized Data". 2006-01. <>.
+ Content History
Submission DateSubmitterOrganization
2012-12-21CWE Content TeamMITRE
New weakness based on discussion on the CWE research list in December 2012.
Modification DateModifierOrganization
2017-11-08CWE Content TeamMITRE
updated Taxonomy_Mappings
2019-01-03CWE Content TeamMITRE
updated Relationships
More information is available — Please select a different filter.
Page Last Updated: January 03, 2019