CWE - CWE-914: Improper Control of Dynamically-Identified Variables (4.16)

Weakness ID: 914

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Base 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.

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Description

The product does not properly restrict reading from or writing to dynamically-identified variables.

Extended Description

Many languages offer powerful features that allow the programmer to access arbitrary variables that are specified by an input string. While these features can offer significant flexibility and reduce development time, they can be extremely dangerous if attackers can modify unintended variables that have security implications.

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
Integrity	Technical Impact: Modify Application Data An attacker could modify sensitive data or program variables.
Integrity	Technical Impact: Execute Unauthorized Code or Commands
Other Integrity	Technical Impact: Varies by Context; Alter Execution Logic

Potential Mitigations

Phase: Implementation

Strategy: Input Validation

For any externally-influenced input, check the input against an allowlist of internal program variables that are allowed to be modified.

Phases: Implementation; Architecture and Design

Strategy: Refactoring

Refactor the code so that internal program variables do not need to be dynamically identified.

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.	99	Improper Control of Resource Identifiers ('Resource Injection')
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.	913	Improper Control of Dynamically-Managed Code Resources
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.	621	Variable Extraction Error
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.	627	Dynamic Variable Evaluation

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

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

Demonstrative Examples

Example 1

This code uses the credentials sent in a POST request to login a user.

(bad code)

Example Language: PHP

//Log user in, and set $isAdmin to true if user is an administrator

function login($user,$pass){

$query = buildQuery($user,$pass);
mysql_query($query);
if(getUserRole($user) == "Admin"){

$isAdmin = true;

}

}

$isAdmin = false;
extract($_POST);
login(mysql_real_escape_string($user),mysql_real_escape_string($pass));

The call to extract() will overwrite the existing values of any variables defined previously, in this case $isAdmin. An attacker can send a POST request with an unexpected third value "isAdmin" equal to "true", thus gaining Admin privileges.

Observed Examples

Reference	Description
CVE-2006-7135	extract issue enables file inclusion
CVE-2006-7079	Chain: extract used for register_globals compatibility layer, enables path traversal (CWE-22)
CVE-2007-0649	extract() buried in include files makes post-disclosure analysis confusing; original report had seemed incorrect.
CVE-2006-6661	extract() enables static code injection
CVE-2006-2828	import_request_variables() buried in include files makes post-disclosure analysis confusing
CVE-2009-0422	Chain: Dynamic variable evaluation allows resultant remote file inclusion and path traversal.
CVE-2007-2431	Chain: dynamic variable evaluation in PHP program used to modify critical, unexpected $_SERVER variable for resultant XSS.
CVE-2006-4904	Chain: dynamic variable evaluation in PHP program used to conduct remote file inclusion.
CVE-2006-4019	Dynamic variable evaluation in mail program allows reading and modifying attachments and preferences of other users.

Weakness Ordinalities

Ordinality	Description
Primary	(where the weakness exists independent of 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.

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1409	Comprehensive Categorization: Injection

Vulnerability Mapping Notes

Usage: ALLOWED

(this CWE ID may 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.

Content History

Submissions
Submission Date	Submitter	Organization
2013-01-26 (CWE 2.4, 2013-02-21)	CWE Content Team	MITRE
2013-01-26 (CWE 2.4, 2013-02-21)
Modifications
Modification Date	Modifier	Organization
2017-01-19	CWE Content Team	MITRE
2017-01-19	updated Relationships
2020-02-24	CWE Content Team	MITRE
2020-02-24	updated Relationships
2020-06-25	CWE Content Team	MITRE
2020-06-25	updated Potential_Mitigations
2023-01-31	CWE Content Team	MITRE
2023-01-31	updated Description
2023-04-27	CWE Content Team	MITRE
2023-04-27	updated Relationships, Time_of_Introduction
2023-06-29	CWE Content Team	MITRE
2023-06-29	updated Mapping_Notes
2023-10-26	CWE Content Team	MITRE
2023-10-26	updated Observed_Examples


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Common Weakness Enumeration

CWE-914: Improper Control of Dynamically-Identified Variables

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