CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-624: Executable Regular Expression Error

Weakness ID: 624
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The product uses a regular expression that either (1) contains an executable component with user-controlled inputs, or (2) allows a user to enable execution by inserting pattern modifiers.
+ Extended Description
Case (2) is possible in the PHP preg_replace() function, and possibly in other languages when a user-controlled input is inserted into a string that is later parsed as a regular expression.
+ Relationships

The table(s) below 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)
+ Relevant to the view "Development Concepts" (CWE-699)
+ 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 software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

PhaseNote
Implementation
+ Applicable Platforms
The listings below show 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)

+ Common Consequences

The table below 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.

ScopeImpactLikelihood
Confidentiality
Integrity
Availability

Technical Impact: Execute Unauthorized Code or Commands

+ Observed Examples
ReferenceDescription
Executable regexp in PHP by inserting "e" modifier into first argument to preg_replace
Executable regexp in PHP by inserting "e" modifier into first argument to preg_replace
Complex curly syntax inserted into the replacement argument to PHP preg_replace(), which uses the "/e" modifier
Function allows remote attackers to execute arbitrary PHP code via the username field, which is used in a preg_replace function call with a /e (executable) modifier.
+ Potential Mitigations

Phase: Implementation

The regular expression feature in some languages allows inputs to be quoted or escaped before insertion, such as \Q and \E in Perl.
+ 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.
NatureTypeIDName
MemberOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
+ Notes

Research Gap

Under-studied. The existing PHP reports are limited to highly skilled researchers, but there are few examples for other languages. It is suspected that this is under-reported for all languages. Usability factors might make it more prevalent in PHP, but this theory has not been investigated.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
Software Fault PatternsSFP24Tainted input to command
+ Content History
Modifications
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Applicable_Platforms, Relationships, Observed_Example
2008-10-14CWE Content TeamMITRE
updated Description
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Relationships
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2014-06-23CWE Content TeamMITRE
updated Observed_Examples
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-11-08CWE Content TeamMITRE
updated Observed_Examples

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Page Last Updated: January 18, 2018