Permissive Regular Expression

The product uses a regular expression that does not sufficiently restrict the set of allowed values.


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



The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following example demonstrates the weakness.

$phone = GetPhoneNumber();
if ($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.

See Also

SFP Secondary Cluster: Tainted Input to Command

This category identifies Software Fault Patterns (SFPs) within the Tainted Input to Command cluster (SFP24).

Data Processing Errors

Weaknesses in this category are typically found in functionality that processes data. Data processing is the manipulation of input to retrieve or save information.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

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