CWE - CWE-627: Dynamic Variable Evaluation (4.18)

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CWE Glossary Definition

CWE-627: Dynamic Variable Evaluation

Weakness ID: 627

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

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Description

In a language where the user can influence the name of a variable at runtime, if the variable names are not controlled, an attacker can read or write to arbitrary variables, or access arbitrary functions.

Extended Description

The resultant vulnerabilities depend on the behavior of the application, both at the crossover point and in any control/data flow that is reachable by the related variables or functions.

Alternate Terms

Dynamic evaluation

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.

Impact	Details
Modify Application Data; Execute Unauthorized Code or Commands	Scope: Confidentiality, Integrity, Availability An attacker could gain unauthorized access to internal program variables and execute arbitrary code.

Potential Mitigations

Phase(s)	Mitigation
Implementation	Strategy: Refactoring Refactor the code to avoid dynamic variable evaluation whenever possible.
Implementation	Strategy: Input Validation Use only allowlists of acceptable variable or function names.
Implementation	For function names, ensure that you are only calling functions that accept the proper number of arguments, to avoid unexpected null arguments.

Relationships

Section Help 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" (View-1000)

Nature	Type	ID	Name
ChildOf	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.	914	Improper Control of Dynamically-Identified Variables
PeerOf	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.	183	Permissive List of Allowed Inputs

Background Details

Many interpreted languages support the use of a "$$varname" construct to set a variable whose name is specified by the $varname variable. In PHP, these are referred to as "variable variables." Functions might also be invoked using similar syntax, such as $$funcname(arg1, arg2).

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.

Phase	Note
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

PHP (Undetermined Prevalence)

Perl (Undetermined Prevalence)

Selected Observed Examples

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Reference	Description
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

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.

Nature	Type	ID	Name
MemberOf	ViewView - 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).	884	CWE Cross-section
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	990	SFP Secondary Cluster: Tainted Input to Command
MemberOf	CategoryCategory - 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 Variant 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.

Notes

Research Gap

Under-studied, probably under-reported. Few researchers look for this issue; most public reports are for PHP, although other languages are affected. This issue is likely to grow in PHP as developers begin to implement functionality in place of register_globals.

References

[REF-517] Steve Christey. "Dynamic Evaluation Vulnerabilities in PHP applications". Full-Disclosure. 2006年05月03日.
<https://seclists.org/fulldisclosure/2006/May/35>. (URL validated: 2023年04月07日)

[REF-518] Shaun Clowes. "A Study In Scarlet: Exploiting Common Vulnerabilities in PHP Applications".
<https://securereality.com.au/study-in-scarlett/>. (URL validated: 2023年04月07日)

Content History

Submissions
Submission Date	Submitter	Organization
2007年05月07日 (CWE Draft 6, 2007年05月07日)	CWE Content Team	MITRE
2007年05月07日 (CWE Draft 6, 2007年05月07日)
Modifications
Modification Date	Modifier	Organization
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated References, Relationships, Type
2020年06月25日	CWE Content Team	MITRE
2020年06月25日	updated Potential_Mitigations
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Relationships
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated References
2014年07月30日	CWE Content Team	MITRE
2014年07月30日	updated Relationships
2013年02月21日	CWE Content Team	MITRE
2013年02月21日	updated Common_Consequences, Observed_Examples, Potential_Mitigations, Relationships, Weakness_Ordinalities
2012年10月30日	CWE Content Team	MITRE
2012年10月30日	updated Potential_Mitigations
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Common_Consequences, Relationships
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2011年03月29日	CWE Content Team	MITRE
2011年03月29日	updated Description
2008年10月14日	CWE Content Team	MITRE
2008年10月14日	updated Background_Details, Description
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Applicable_Platforms, Relationships
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Time_of_Introduction

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Page Last Updated: September 09, 2025

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