CWE-185: Incorrect Regular Expression

Code Examples & CVEs

Demonstrative Examples

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

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.

BadPerl

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

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

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.

BadPython

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)

Observed CVE Examples (11)

CVE-2002-2109

Regexp isn't "anchored" to the beginning or end, which allows spoofed values that have trusted values as substrings.

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CVE-2005-1949

Regexp for IP address isn't anchored at the end, allowing appending of shell metacharacters.

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CVE-2001-1072

Bypass access restrictions via multiple leading slash, which causes a regular expression to fail.

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CVE-2000-0115

Local user DoS via invalid regular expressions.

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CVE-2002-1527

chain: Malformed input generates a regular expression error that leads to information exposure.

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CVE-2005-1061

Certain strings are later used in a regexp, leading to a resultant crash.

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CVE-2005-2169

MFV. Regular expression intended to protect against directory traversal reduces ".../...//" to "../".

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CVE-2005-0603

Malformed regexp syntax leads to information exposure in error message.

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CVE-2005-1820

Code injection due to improper quoting of regular expression.

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CVE-2005-3153

Null byte bypasses PHP regexp check.

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CVE-2005-4155

Null byte bypasses PHP regexp check.

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Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-185 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-185, Incorrect Regular Expression, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Apply Refactoring controls for Incorrect Regular Expression

MITRE associates mitigation with Implementation; the listed strategies include Refactoring; documented detection approaches include Automated Static Analysis. Use these source-defined anchors to turn CWE-185 into implementation, review, and verification checks for the affected component.

CWE-185: Incorrect Regular Expression — MITRE CWE

Triage CWE-185 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-185, Incorrect Regular Expression, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-185

Apply MITRE's full root-cause mapping guidance when using CWE-185, Incorrect Regular Expression. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-185 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-185, Incorrect Regular Expression. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-185: Incorrect Regular Expression?+

CWE-185: Incorrect Regular Expression is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product specifies a regular expression in a way that causes data to be improperly matched or compared. When the regular expression is used in protection mechanisms such as filtering or validation, this may allow an attacker to bypass the intended restrictions on the incoming data.

What are the security consequences of Incorrect Regular Expression?+

If exploited, CWE-185 (Incorrect Regular Expression) it can compromise Other and Access Control, leading to outcomes such as Unexpected State, Varies by Context and Bypass Protection Mechanism.

Which programming languages are affected by Incorrect Regular Expression?+

CWE-185 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Incorrect Regular Expression?+

MITRE documents real CVEs mapped to CWE-185, including CVE-2002-2109, CVE-2005-1949, CVE-2001-1072, CVE-2000-0115 and CVE-2002-1527. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-185 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-185: Incorrect Regular Expression

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Scope

Impact

Mitigation Strategies

Detection Methods

Code Examples & CVEs

Demonstrative Examples

Observed CVE Examples (11)

CWE Relationships

Parent Weaknesses

Source-backed guidance

Verify controls for CWE-185 with SSDF evidence

Apply Refactoring controls for Incorrect Regular Expression

Triage CWE-185 against known exploitation evidence

Apply precise root-cause mapping to CWE-185

Validate CWE-185 with root-cause mapping checks

Frequently Asked Questions

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