CWE - CWE-181: Incorrect Behavior Order: Validate Before Filter (4.18)

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CWE Glossary Definition

CWE-181: Incorrect Behavior Order: Validate Before Filter

Weakness ID: 181

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

The product validates data before it has been filtered, which prevents the product from detecting data that becomes invalid after the filtering step.

Extended Description

This can be used by an attacker to bypass the validation and launch attacks that expose weaknesses that would otherwise be prevented, such as injection.

Alternate Terms

Validate-before-cleanse

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
Bypass Protection Mechanism	Scope: Access Control

Potential Mitigations

Phase(s)	Mitigation
Implementation; Architecture and Design	Inputs should be decoded and canonicalized to the application's current internal representation before being filtered.

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.	179	Incorrect Behavior Order: Early Validation

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

Class: Not Language-Specific (Undetermined Prevalence)

Demonstrative Examples

Example 1

This script creates a subdirectory within a user directory and sets the user as the owner.

(bad code)

Example Language: PHP

function createDir($userName,$dirName){

$userDir = '/users/'. $userName;
if(strpos($dirName,'..') !== false){

echo 'Directory name contains invalid sequence';
return;

}
//filter out '~' because other scripts identify user directories by this prefix
$dirName = str_replace('~','',$dirName);
$newDir = $userDir . $dirName;
mkdir($newDir, 0700);
chown($newDir,$userName);

}

While the script attempts to screen for '..' sequences, an attacker can submit a directory path including ".~.", which will then become ".." after the filtering step. This allows a Path Traversal (CWE-21) attack to occur.

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-2002-0934	Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.
CVE-2003-0282	Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.

Functional Areas

Protection Mechanism

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	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	722	OWASP Top Ten 2004 Category A1 - Unvalidated Input
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	992	SFP Secondary Cluster: Faulty Input Transformation
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1410	Comprehensive Categorization: Insufficient Control Flow Management

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

This category is probably under-studied.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
PLOVER	Validate-Before-Filter
OWASP Top Ten 2004	A1	CWE More Specific	Unvalidated Input

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-120	Double Encoding
CAPEC-267	Leverage Alternate Encoding
CAPEC-3	Using Leading 'Ghost' Character Sequences to Bypass Input Filters
CAPEC-43	Exploiting Multiple Input Interpretation Layers
CAPEC-78	Using Escaped Slashes in Alternate Encoding
CAPEC-79	Using Slashes in Alternate Encoding
CAPEC-80	Using UTF-8 Encoding to Bypass Validation Logic

Content History

Submissions
Submission Date	Submitter	Organization
2006年07月19日 (CWE Draft 3, 2006年07月19日)	PLOVER
2006年07月19日 (CWE Draft 3, 2006年07月19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 Relationships
2023年01月31日	CWE Content Team	MITRE
2023年01月31日	updated Description
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Relationships, Type
2019年01月03日	CWE Content Team	MITRE
2019年01月03日	updated Related_Attack_Patterns
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Applicable_Platforms
2017年01月19日	CWE Content Team	MITRE
2017年01月19日	updated Relationships
2014年07月30日	CWE Content Team	MITRE
2014年07月30日	updated Relationships
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 Demonstrative_Examples, Observed_Examples, Related_Attack_Patterns, 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 Demonstrative_Examples
2010年06月21日	CWE Content Team	MITRE
2010年06月21日	updated Description, Observed_Examples
2008年10月14日	CWE Content Team	MITRE
2008年10月14日	updated Description
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Functional_Areas, Relationships, Research_Gaps, Taxonomy_Mappings, Type
2008年08月15日	Veracode
2008年08月15日	Suggested OWASP Top Ten 2004 mapping
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Potential_Mitigations, Time_of_Introduction
Previous Entry Names
Change Date	Previous Entry Name
2008年04月11日	Validate-before-filter

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Page Last Updated: September 09, 2025

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