Common Weakness Enumeration

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CWE-914: Improper Control of Dynamically-Identified Variables

Weakness ID: 914
Abstraction: Base
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software 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.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Common Consequences

Technical Impact: Modify application data

An attacker could modify sensitive data or program variables.


Technical Impact: Execute unauthorized code or commands


Technical Impact: Varies by context; Alter execution logic

+ 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,$pass);
if(getUserRole($user) == "Admin"){
$isAdmin = true;

$isAdmin = false;

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
extract issue enables file inclusion
extract used for register_globals compatibility layer, enables path traversal
extract() buried in include files makes post-disclosure analysis confusing; original report had seemed incorrect.
extract() enables static code injection
import_request_variables() buried in include files makes post-disclosure analysis confusing
Chain: Dynamic variable evaluation allows resultant remote file inclusion and path traversal.
Chain: dynamic variable evaluation in PHP program used to modify critical, unexpected $_SERVER variable for resultant XSS.
Chain: dynamic variable evaluation in PHP program used to conduct remote file inclusion.
Dynamic variable evaluation in mail program allows reading and modifying attachments and preferences of other users.
+ Potential Mitigations

Phase: Implementation

Strategy: Input Validation

For any externally-influenced input, check the input against a white list 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.

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base99Improper Control of Resource Identifiers ('Resource Injection')
Development Concepts699
Research Concepts (primary)1000
ChildOfWeakness ClassWeakness Class913Improper Control of Dynamically-Managed Code Resources
Development Concepts (primary)699
Research Concepts1000
ParentOfWeakness BaseWeakness Base621Variable Extraction Error
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base627Dynamic Variable Evaluation
Development Concepts (primary)699
Research Concepts (primary)1000
+ Content History
Submission DateSubmitterOrganizationSource
2013-01-26MITREInternal CWE Team
Modification DateModifierOrganizationSource
2017-01-19CWE Content TeamMITREInternal
updated Relationships

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Page Last Updated: May 05, 2017