CWE-57: Path Equivalence: 'fakedir/../realdir/filename'

What is Path Equivalence: 'fakedir/../realdir/filename'?

• Overview: This vulnerability occurs when protection mechanisms intended to restrict access to certain files are bypassed due to improper handling of pathnames like 'fakedir/../realdir/filename'. When the system receives a path with directory traversal sequences such as '../', it may not correctly resolve the path, allowing unauthorized access.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting input that includes directory traversal sequences to access restricted files.
• Common attack patterns include sending requests with manipulated pathnames to trick the system into resolving to sensitive files.

• Security Impact:

• Direct consequences include unauthorized access to protected files and directories, leading to potential data breaches.
• Potential cascading effects include further exploitation of sensitive data and system compromise.
• Business impact can range from loss of customer trust to legal repercussions and financial losses due to data exposure.

• Prevention Guidelines:

• Specific code-level fixes include normalizing and validating path inputs to ensure they don't contain directory traversal sequences.
• Security best practices involve implementing strict access control measures and input validation routines.
• Recommended tools and frameworks include using libraries and APIs that handle path normalization securely and conducting regular security audits to detect vulnerabilities.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

const path = require('path');
const fs = require('fs');

function readFile(userInputPath) {
    const baseDirectory = '/secure/data';
    // Vulnerable: Directly concatenating user input with the base directory
    // This allows path traversal using paths like 'fakedir/../realdir/filename'
    const filePath = path.join(baseDirectory, userInputPath);
    return fs.readFileSync(filePath, 'utf8');
}

// Example of a dangerous user input: 'fakedir/../realdir/filename'
const userInput = 'fakedir/../realdir/filename';
const data = readFile(userInput);

How to fix Path Equivalence: 'fakedir/../realdir/filename'?

To prevent path traversal in JavaScript, you should:

1. Normalize the Path: Use path.normalize() to remove any potential path traversal sequences.
2. Validate the Path: Ensure the resulting path is still within the intended base directory using path.resolve() and startsWith().
3. Reject Invalid Paths: If the resolved path doesn't start with the base directory, deny access.

Fixed Code Example

const path = require('path');
const fs = require('fs');

function readFile(userInputPath) {
    const baseDirectory = path.resolve('/secure/data');
    // Normalize the user input path to prevent path traversal
    const normalizedPath = path.normalize(userInputPath);
    // Construct the full file path
    const filePath = path.resolve(baseDirectory, normalizedPath);
    // Verify that the file path is within the intended directory
    if (!filePath.startsWith(baseDirectory)) {
        throw new Error('Access to the file is denied: Invalid path.');
    }
    return fs.readFileSync(filePath, 'utf8');
}

// Example of sanitized user input
const userInput = 'fakedir/../realdir/filename';
try {
    const data = readFile(userInput);
} catch (error) {
    console.error(error.message);
}

These examples demonstrate how to handle path equivalence vulnerabilities by ensuring that user inputs are sanitized and validated before being used in file path operations, preventing unauthorized file access. The fixed code ensures that any attempts to traverse directories outside the intended base directory are blocked, maintaining the security of the file access operation.