CWE

Common Weakness Enumeration

A community-developed list of SW & HW weaknesses that can become vulnerabilities

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ID

CWE-908: Use of Uninitialized Resource

Weakness ID: 908
Vulnerability Mapping: ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities
Abstraction: BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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+ Description
The product uses or accesses a resource that has not been initialized.
+ Extended Description
When a resource has not been properly initialized, the product may behave unexpectedly. This may lead to a crash or invalid memory access, but the consequences vary depending on the type of resource and how it is used within the product.
+ Common Consequences
Section HelpThis table 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.
ScopeImpactLikelihood
Confidentiality

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.
Availability

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.
+ 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 product with settings that generate warnings about uninitialized variables or data.
+ Relationships
Section HelpThis table 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)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.665Improper Initialization
ParentOfVariantVariant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.457Use of Uninitialized Variable
CanFollowClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.909Missing Initialization of Resource
Section HelpThis table 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 "Software Development" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.399Resource Management Errors
Section HelpThis table 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 "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.665Improper Initialization
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
PhaseNote
Implementation
+ Applicable Platforms
Section HelpThis listing shows 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.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

+ Likelihood Of Exploit
Medium
+ 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) {
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.


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.


Example 4

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.

(bad code)
Example Language:
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:

(good code)
Example Language:
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:

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

+ Observed Examples
ReferenceDescription
Chain: Creation of the packet client occurs before initialization is complete (CWE-696) resulting in a read from uninitialized memory (CWE-908), causing memory corruption.
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.
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
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
+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
+ Memberships
Section HelpThis 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.
NatureTypeIDName
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)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1306CISQ Quality Measures - Reliability
MemberOfViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries).1340CISQ Data Protection Measures
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1416Comprehensive Categorization: Resource Lifecycle Management
+ Vulnerability Mapping Notes

Usage: ALLOWED

(this CWE ID could be used to map to real-world vulnerabilities)

Reason: Acceptable-Use

Rationale:

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments:

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
+ 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. <http://www.felinemenace.org/~mercy/papers/UBehavior/UBehavior.zip>.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2012-12-21
(CWE 2.4, 2013-02-21)
CWE Content TeamMITRE
New weakness based on discussion on the CWE research list in December 2012.
+ Modifications
Modification DateModifierOrganization
2017-11-08CWE Content TeamMITRE
updated Taxonomy_Mappings
2019-01-03CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Description, Relationships
2020-08-20CWE Content TeamMITRE
updated Relationships
2020-12-10CWE Content TeamMITRE
updated Relationships
2021-03-15CWE Content TeamMITRE
updated Demonstrative_Examples, Observed_Examples
2023-01-31CWE Content TeamMITRE
updated Description, Potential_Mitigations
2023-04-27CWE Content TeamMITRE
updated Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes
Page Last Updated: July 16, 2024