CWE-625: Permissive Regular Expression

Description

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

Submission Date :

May 7, 2007, midnight

Modification Date :

2023-06-29 00:00:00+00:00

Organization :

MITRE
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

Example Vulnerable Codes

Example - 1

The following code takes phone numbers as input, and uses a regular expression to reject invalid phone numbers.


// # looks like it only has hyphens and digits// 
system("lookup-phone $phone");
error("malformed number!");$phone = GetPhoneNumber();if ($phone =~ /\d+-\d+/) {}else {}

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.

Example - 2

This code uses a regular expression to validate an IP string prior to using it in a call to the "ping" command.




return ip

raise ValueError("IP address does not match valid pattern.")ip_validator = re.compile(r"((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4}")if ip_validator.match(ip):else:

// # The ping command treats zero-prepended IP addresses as octal// 
validated = validate_ip_regex(ip)result = subprocess.call(["ping", validated])print(result)import subprocessimport redef validate_ip_regex(ip: str):def run_ping_regex(ip: str):

Since the regular expression does not have anchors (CWE-777), i.e. is unbounded without ^ or $ characters, then prepending a 0 or 0x to the beginning of the IP address will still result in a matched regex pattern. Since the ping command supports octal and hex prepended IP addresses, it will use the unexpectedly valid IP address (CWE-1389). For example, "0x63.63.63.63" would be considered equivalent to "99.63.63.63". As a result, the attacker could potentially ping systems that the attacker cannot reach directly.

Related Weaknesses

This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined to give an overview of the different insight to similar items that may exist at higher and lower levels of abstraction.

Visit http://cwe.mitre.org/ for more details.

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