CWE - CWE-909: Missing Initialization of Resource (4.5)

Weakness ID: 909

Abstraction: Base
Structure: Simple

Status: Incomplete

Presentation Filter:

Description

The software does not initialize a critical resource.

Extended Description

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.

Relationships

This 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)

Nature	Type	ID	Name
ChildOf	Class - 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.	665	Improper Initialization
ParentOf	Variant - 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.	456	Missing Initialization of a Variable
CanPrecede	Base - 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.	908	Use of Uninitialized Resource

Relevant to the view "Software Development" (CWE-699)

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	399	Resource Management Errors

Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)

Nature	Type	ID	Name
ChildOf	Class - 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.	665	Improper Initialization

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 life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Implementation

Applicable Platforms

This 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: Language-Independent (Undetermined Prevalence)

Common Consequences

This 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.

Scope	Impact	Likelihood
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.

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: C

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: C

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: C

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: C

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

Reference	Description
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-2005-1036	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

Potential Mitigations

Phase: Implementation

Explicitly initialize the resource before use. If this is performed through an API function or standard procedure, follow all specified 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 your software with settings that generate warnings about uninitialized variables or data.

Weakness Ordinalities

Ordinality	Description
Primary	(where the weakness exists independent of other weaknesses)
Resultant	(where the weakness is typically related to the presence of some other weaknesses)

Content History

Submissions
Submission Date	Submitter	Organization
2012-12-21	CWE Content Team	MITRE
2012-12-21	New weakness based on discussion on the CWE research list in December 2012.
Modifications
Modification Date	Modifier	Organization
2019-06-20	CWE Content Team	MITRE
2019-06-20	updated Relationships
2020-02-24	CWE Content Team	MITRE
2020-02-24	updated Relationships
2021-03-15	CWE Content Team	MITRE
2021-03-15	updated Demonstrative_Examples, Observed_Examples


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Common Weakness Enumeration

CWE-909: Missing Initialization of Resource