What is Path Equivalence (CWE-47)?

AI-friendly summary

TL;DR: Path Equivalence (CWE-47) is a type of vulnerability that occurs when a product accepts path input in the form of leading space (‘ filedir’) without appropriate validation, which can lead to ambiguous path resolution and allow an attacker to traverse the file system to unintended locations or access arbitrary files. To fix this issue, you should validate and sanitize user input, use a secure library for file operations, and configure your web server securely.

Quick Summary

Path Equivalence (CWE-47) is a type of vulnerability that occurs when a product accepts path input in the form of leading space (‘ filedir’) without appropriate validation. This can lead to ambiguous path resolution and allow an attacker to traverse the file system to unintended locations or access arbitrary files. The consequences of Path Equivalence include read files or directories and modify files or directories.

Jump to: Quick Summary · What is Path Equivalence? · Path Equivalence Overview · How Path Equivalence Works · Business Impact of Path Equivalence · Path Equivalence Attack Scenario · How to Detect Path Equivalence · How to Fix Path Equivalence · Framework-Specific Fixes for Path Equivalence · How to Ask AI to Check Your Code for Path Equivalence · Path Equivalence Best Practices Checklist · Path Equivalence FAQ · Vulnerabilities Related to Path Equivalence · References · Scan Your Own Site

What is Path Equivalence?

Path Equivalence (CWE-47) is a type of vulnerability that occurs when a product accepts path input in the form of leading space (‘ filedir’) without appropriate validation. As defined by the MITRE Corporation under CWE-47, and classified by the OWASP Foundation as Not directly mapped, this vulnerability can have significant business impacts.

Path Equivalence Overview

What: Path Equivalence (CWE-47) occurs when a product accepts path input in the form of leading space (‘ filedir’) without appropriate validation. Why it matters: The consequences of Path Equivalence include read files or directories and modify files or directories. This vulnerability can have significant business impacts, including financial losses, compliance issues, and reputational damage. Where it occurs: Path Equivalence typically occurs in web applications that handle user input for file paths or directory traversal. Who is affected: Any organization that handles sensitive data or has a web application that accepts path input from users may be affected by this vulnerability. Who is NOT affected: Applications that never construct paths/queries/commands from external input, or systems already using secure libraries for file operations and configuring their web servers securely.

How Path Equivalence Works

Root Cause

The root cause of Path Equivalence (CWE-47) is the lack of validation and sanitization of user input for path resolution. This allows an attacker to traverse the file system to unintended locations or access arbitrary files.

Attack Flow

1. The attacker sends a malicious request with leading space (‘ filedir’) in the path input.
2. The web application accepts the path input without proper validation, allowing the attacker to bypass security checks.
3. The attacker gains access to sensitive data or files, or modifies existing files.

Prerequisites to Exploit

For this vulnerability to be exploitable, the following conditions must be true:

• The web application accepts user input for file paths or directory traversal.
• The user input is not properly validated and sanitized.
• The attacker has knowledge of the file system structure and can craft a malicious request.

Vulnerable Code

import os

path = request.form['filedir']
os.chdir(path)

This code demonstrates the vulnerability by accepting user input for path resolution without proper validation. The os.chdir() function changes the current working directory to the specified path, allowing the attacker to traverse the file system.

Secure Code

import os

path = request.form['filedir']
if not os.path.abspath(path).startswith(base_dir):
    raise ValueError('Invalid path')
else:
    os.chdir(path)

This code demonstrates a secure implementation by validating and sanitizing user input for path resolution. The os.path.abspath() function ensures the path is absolute, and the startswith() method checks if the path starts with the allowed base directory.

Business Impact of Path Equivalence

The consequences of Path Equivalence (CWE-47) include:

• Confidentiality: Sensitive data or files may be accessed by unauthorized users.
• Integrity: Existing files may be modified or deleted by attackers.
• Availability: The web application may become unavailable due to excessive resource usage or file system corruption.

The business impacts of Path Equivalence can be significant, including financial losses, compliance issues, and reputational damage. Organizations should prioritize fixing this vulnerability to prevent these consequences.

Path Equivalence Attack Scenario

Here is a step-by-step walkthrough of an attack scenario:

1. The attacker crafts a malicious request with leading space (‘ filedir’) in the path input.
2. The web application accepts the path input without proper validation, allowing the attacker to bypass security checks.
3. The attacker gains access to sensitive data or files, or modifies existing files.

How to Detect Path Equivalence

Manual Testing

To detect Path Equivalence (CWE-47) manually, follow these steps:

• Review web application code for path input handling.
• Test user input for leading space (‘ filedir’) in the path resolution process.
• Verify if security checks are bypassed when malicious requests are sent.

Automated Scanners (SAST / DAST)

Automated scanners can detect Path Equivalence by analyzing web application code and identifying potential vulnerabilities. However, dynamic testing is required to confirm the presence of this vulnerability.

PenScan Detection

PenScan’s scanner engines actively test for this issue by simulating malicious requests with leading space (‘ filedir’) in the path input.

False Positive Guidance

To avoid false positives when detecting Path Equivalence:

• Verify if security checks are bypassed when malicious requests are sent.
• Check if user input is properly validated and sanitized before path resolution.

How to Fix Path Equivalence

To fix Path Equivalence (CWE-47), follow these steps:

• Validate and sanitize user input for path resolution using secure libraries.
• Configure web servers securely to prevent bypassing security checks.
• Implement additional security measures, such as access control lists or file system permissions, to restrict access to sensitive data or files.

Framework-Specific Fixes for Path Equivalence

Java

import java.io.File;

String path = request.getParameter('filedir');
File file = new File(path);
if (!file.getAbsoluteFile().getPath().startsWith(baseDir)) {
    throw new SecurityException("Invalid path");
}

Node.js

const fs = require('fs');

let path = req.body.filedir;
let file = fs.statSync(path);
if (!file.absolutePath.startsWith(baseDir)) {
    throw new Error("Invalid path");
}

Python/Django

import os

path = request.POST['filedir']
if not os.path.abspath(path).startswith(base_dir):
    raise ValueError('Invalid path')

How to Ask AI to Check Your Code for Path Equivalence

To ask an AI coding assistant to review your code for potential CWE-47 Path Equivalence vulnerabilities, use the following prompt:

Review the following [language] code block for potential CWE-47 Path Equivalence vulnerabilities and rewrite it using primary fix techniques: [paste code here]

Path Equivalence Best Practices Checklist

✅ Validate and sanitize user input for path resolution. ✅ Configure web servers securely to prevent bypassing security checks. ✅ Implement additional security measures, such as access control lists or file system permissions, to restrict access to sensitive data or files.

Path Equivalence FAQ

How does Path Equivalence work?

Path Equivalence (CWE-47) occurs when a product accepts path input in the form of leading space (‘ filedir’) without appropriate validation, which can lead to ambiguous path resolution and allow an attacker to traverse the file system to unintended locations or access arbitrary files.

What are the consequences of Path Equivalence?

The consequences of Path Equivalence include read files or directories and modify files or directories.

How do I detect Path Equivalence in my application?

You can detect Path Equivalence by using automated scanners, manual testing, or PenScan’s detection capabilities.

What is the best way to fix Path Equivalence?

The best way to fix Path Equivalence is to validate and sanitize user input, use a secure library for file operations, and configure your web server securely.

Can I use AI to check my code for Path Equivalence?

Yes, you can use AI coding assistants to review your code for potential CWE-47 Path Equivalence vulnerabilities and rewrite it using primary fix techniques.

What are some best practices for preventing Path Equivalence?

Some best practices for preventing Path Equivalence include validating and sanitizing user input, using a secure library for file operations, configuring your web server securely, and following framework-specific guidelines.

Vulnerabilities Related to Path Equivalence

References

• MITRE CWE-47
• CAPEC
• NVD

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Path Equivalence and other risks before an attacker does.