include::../description.adoc[]

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== Recommended Secure Coding Practices

Check whether your regular expression engine (the algorithm executing your regular expression) has any known vulnerabilities. Search for vulnerability reports mentioning the one engine you're are using.


If the regular expression is vulnerable to ReDos attacks, mitigate the risk by using a "match timeout" to limit the time spent running the regular expression.


Remember also that a ReDos attack is possible if a user-provided regular expression is executed. This rule won't detect this kind of injection.

== Sensitive Code Example

----
Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Runtime.Serialization
Imports System.Text.RegularExpressions
Imports System.Web

Namespace N
    Public Class RegularExpression
        Private Sub Foo(ByVal pattern As String, ByVal options As RegexOptions, ByVal matchTimeout As TimeSpan,
                        ByVal input As String, ByVal replacement As String, ByVal evaluator As MatchEvaluator)
            ' All the following instantiations are Sensitive. Validate the regular expression and matched input.
            Dim r As Regex = New System.Text.RegularExpressions.Regex("(a+)+b")
            r = New System.Text.RegularExpressions.Regex("(a+)+b", options)
            r = New System.Text.RegularExpressions.Regex("(a+)+b", options, matchTimeout)

            ' All the following static methods are Sensitive.
            System.Text.RegularExpressions.Regex.IsMatch(input, "(a+)+b")
            System.Text.RegularExpressions.Regex.IsMatch(input, "(a+)+b", options)
            System.Text.RegularExpressions.Regex.IsMatch(input, "(a+)+b", options, matchTimeout)

            System.Text.RegularExpressions.Regex.Match(input, "(a+)+b")
            System.Text.RegularExpressions.Regex.Match(input, "(a+)+b", options)
            System.Text.RegularExpressions.Regex.Match(input, "(a+)+b", options, matchTimeout)

            System.Text.RegularExpressions.Regex.Matches(input, "(a+)+b")
            System.Text.RegularExpressions.Regex.Matches(input, "(a+)+b", options)
            System.Text.RegularExpressions.Regex.Matches(input, "(a+)+b", options, matchTimeout)

            System.Text.RegularExpressions.Regex.Replace(input, "(a+)+b", evaluator)
            System.Text.RegularExpressions.Regex.Replace(input, "(a+)+b", evaluator, options)
            System.Text.RegularExpressions.Regex.Replace(input, "(a+)+b", evaluator, options, matchTimeout)
            System.Text.RegularExpressions.Regex.Replace(input, "(a+)+b", replacement)
            System.Text.RegularExpressions.Regex.Replace(input, "(a+)+b", replacement, options)
            System.Text.RegularExpressions.Regex.Replace(input, "(a+)+b", replacement, options, matchTimeout)

            System.Text.RegularExpressions.Regex.Split(input, "(a+)+b")
            System.Text.RegularExpressions.Regex.Split(input, "(a+)+b", options)
            System.Text.RegularExpressions.Regex.Split(input, "(a+)+b", options, matchTimeout)
        End Sub
    End Class
End Namespace
----

include::../exceptions.adoc[]

include::../see.adoc[]

ifdef::env-github,rspecator-view[]
'''
== Comments And Links
(visible only on this page)

include::../comments-and-links.adoc[]
endif::env-github,rspecator-view[]
