CWE-625: Permissive Regular ExpressionWeakness ID: 625 Vulnerability Mapping:
ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction: BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. |
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
Common Consequences This table 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.Scope | Impact | Likelihood |
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Access Control
| Technical Impact: Bypass Protection Mechanism | |
Potential Mitigations
Phase: Implementation When applicable, ensure that the regular expression marks beginning and ending string patterns, such as "/^string$/" for Perl. |
Relationships This table 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) Nature | Type | ID | Name |
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ChildOf | Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. | 185 | Incorrect Regular Expression | ParentOf | Variant - a weakness
that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. | 777 | Regular Expression without Anchors | PeerOf | Base - a weakness
that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. | 183 | Permissive List of Allowed Inputs | PeerOf | Base - a weakness
that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. | 184 | Incomplete List of Disallowed Inputs | PeerOf | Variant - a weakness
that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. | 187 | Partial String Comparison |
This table 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 "Software Development" (CWE-699) Nature | Type | ID | Name |
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MemberOf | Category - a CWE entry that contains a set of other entries that share a common characteristic. | 19 | Data Processing Errors |
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 life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.Phase | Note |
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Implementation | This problem is frequently found when the regular expression is used in input validation or security features such as authentication. |
Demonstrative Examples Example 1 The following code takes phone numbers as input, and uses a regular expression to reject invalid phone numbers. (bad code) 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. Example 2 This code uses a regular expression to validate an IP string prior to using it in a call to the "ping" command. (bad code) Example Language: Python
import subprocess
import re
def validate_ip_regex(ip: str):
ip_validator = re.compile(r"((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4}")
if ip_validator.match(ip):
return ip
else:
raise ValueError("IP address does not match valid pattern.")
def run_ping_regex(ip: str):
validated = validate_ip_regex(ip)
# The ping command treats zero-prepended IP addresses as octal
result = subprocess.call(["ping", validated])
print(result)
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. Observed Examples Reference | Description |
| Chain: regex in EXIF processor code does not correctly determine where a string ends ( CWE-625), enabling eval injection ( CWE-95), as exploited in the wild per CISA KEV. |
| ".*" 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. |
Weakness Ordinalities Ordinality | Description |
Primary | (where the weakness exists independent of other weaknesses) |
Detection Methods
Automated Static Analysis Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.) |
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. Vulnerability Mapping Notes Usage: ALLOWED (this CWE ID could be used to map to real-world vulnerabilities) | Reason: Acceptable-Use | Rationale: This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities. | Comments: Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction. |
Taxonomy Mappings Mapped Taxonomy Name | Node ID | Fit | Mapped Node Name |
The CERT Oracle Secure Coding Standard for Java (2011) | IDS08-J | | Sanitize 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.
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Content History Submissions |
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Submission Date | Submitter | Organization |
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2007-05-07 (CWE Draft 6, 2007-05-07) | CWE Content Team | MITRE | | Modifications |
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Modification Date | Modifier | Organization |
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2008-07-01 | Eric Dalci | Cigital | updated Time_of_Introduction | 2008-09-08 | CWE Content Team | MITRE | updated Applicable_Platforms, Description, Relationships, Observed_Example, Other_Notes, Weakness_Ordinalities | 2009-03-10 | CWE Content Team | MITRE | updated Description | 2009-05-27 | CWE Content Team | MITRE | updated Demonstrative_Examples | 2009-07-27 | CWE Content Team | MITRE | updated Relationships | 2011-06-01 | CWE Content Team | MITRE | updated Common_Consequences, Relationships, Taxonomy_Mappings | 2012-05-11 | CWE Content Team | MITRE | updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings | 2012-10-30 | CWE Content Team | MITRE | updated Potential_Mitigations | 2014-06-23 | CWE Content Team | MITRE | updated Modes_of_Introduction, Other_Notes | 2014-07-30 | CWE Content Team | MITRE | updated Relationships | 2017-11-08 | CWE Content Team | MITRE | updated Demonstrative_Examples, Observed_Examples | 2019-01-03 | CWE Content Team | MITRE | updated Taxonomy_Mappings | 2020-02-24 | CWE Content Team | MITRE | updated Relationships | 2021-03-15 | CWE Content Team | MITRE | updated Demonstrative_Examples | 2022-06-28 | CWE Content Team | MITRE | updated Observed_Examples | 2022-10-13 | CWE Content Team | MITRE | updated Demonstrative_Examples | 2023-04-27 | CWE Content Team | MITRE | updated Detection_Factors, Relationships | 2023-06-29 | CWE Content Team | MITRE | updated Mapping_Notes |
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