Common Weakness Enumeration

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CWE-625: Permissive Regular Expression

Weakness ID: 625
Abstraction: Base
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The product uses a regular expression that does not sufficiently restrict the set of allowed values.
+ Extended Description

This effectively causes the regexp to accept substrings that match the pattern, which produces a partial comparison to the target. In some cases, this can lead to other weaknesses. Common errors include:

  • not identifying the beginning and end of the target string
  • using wildcards instead of acceptable character ranges
  • others
+ 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)
ChildOfClassClass185Incorrect Regular Expression
ParentOfVariantVariant777Regular Expression without Anchors
PeerOfBaseBase183Permissive Whitelist
PeerOfBaseBase184Incomplete Blacklist
PeerOfBaseBase187Partial Comparison
+ Relevant to the view "Development Concepts" (CWE-699)
ChildOfClassClass185Incorrect Regular Expression
ParentOfVariantVariant777Regular Expression without Anchors
+ 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.

ImplementationThis problem is frequently found when the regular expression is used in input validation or security features such as authentication.
+ 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.


Perl: (Undetermined Prevalence)

PHP: (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.

Access Control

Technical Impact: Bypass Protection Mechanism

+ Demonstrative Examples

Example 1

The following example demonstrates the weakness.

Example Language: Perl 
$phone = GetPhoneNumber();
if ($phone =~ /\d+-\d+/) {
# looks like it only has hyphens and digits
system("lookup-phone $phone");

else {
error("malformed number!");


An attacker could provide an argument such as: "; ls -l ; echo 123-456" This would pass the check, since "123-456" is sufficient to match the "\d+-\d+" portion of the regular expression.

+ Observed Examples
".*" regexp leads to static code injection
insertion of username into regexp results in partial comparison, causing wrong database entry to be updated when one username is a substring of another.
regexp intended to verify that all characters are legal, only checks that at least one is legal, enabling file inclusion.
Regexp for IP address isn't anchored at the end, allowing appending of shell metacharacters.
Regexp isn't "anchored" to the beginning or end, which allows spoofed values that have trusted values as substrings.
regexp in .htaccess file allows access of files whose names contain certain substrings
allow load of macro files whose names contain certain substrings.
+ Potential Mitigations

Phase: Implementation

When applicable, ensure that the regular expression marks beginning and ending string patterns, such as "/^string$/" for Perl.
+ Weakness Ordinalities
(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.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CERT Java Secure CodingIDS08-JSanitize untrusted data passed to a regex
+ References
[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 8, "Character Stripping Vulnerabilities", Page 437.. 1st Edition. Addison Wesley. 2006.
+ Content History
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Applicable_Platforms, Description, Relationships, Observed_Example, Other_Notes, Weakness_Ordinalities
2009-03-10CWE Content TeamMITRE
updated Description
2009-05-27CWE Content TeamMITRE
updated Demonstrative_Examples
2009-07-27CWE Content TeamMITRE
updated Relationships
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2014-06-23CWE Content TeamMITRE
updated Modes_of_Introduction, Other_Notes
2014-07-30CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Demonstrative_Examples, Observed_Examples

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Page Last Updated: November 14, 2017