CWE-24: Path Traversal: '../filedir'

What is Path Traversal: '../filedir'?

• Overview: Path Traversal (CWE-24) is a security vulnerability where an application improperly handles user input used in file paths, allowing attackers to navigate outside of the intended directory and access restricted files or directories.

• Exploitation Methods:

• Attackers exploit this vulnerability by injecting "../" sequences in user inputs to navigate the file system.
• Common attack patterns involve appending "../" to input fields that influence file paths, thereby bypassing directory restrictions.

• Security Impact:

• Direct consequences include unauthorized access to sensitive files and directories.
• Potential cascading effects involve further system compromises if critical configuration files or scripts are accessed and modified.
• Business impact includes data breaches, loss of sensitive information, reputational damage, and potential legal consequences.

• Prevention Guidelines:

• Specific code-level fixes include validating and sanitizing file path inputs to remove or neutralize "../" sequences.
• Security best practices involve using APIs that abstract file system interactions and automatically handle path resolution securely.
• Recommended tools and frameworks include those with built-in path validation features, such as using realpath() functions in the appropriate programming languages to resolve paths safely.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

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

function readFile(filename) {
    // Vulnerable to Path Traversal: The filename is directly used to create the file path
    const baseDirectory = '/var/www/uploads/';
    const filePath = path.join(baseDirectory, filename); // Unsafe: User input directly influences the file path
    return fs.readFileSync(filePath, 'utf8'); // Potentially dangerous file access
}

// Example of dangerous input: "../../etc/passwd"
console.log(readFile("../../etc/passwd"));

How to fix Path Traversal: '../filedir'?

To prevent path traversal in JavaScript, especially in Node.js environments:

1. Validate and sanitize inputs: Ensure the input does not contain unauthorized directory traversal patterns.
2. Use secure path resolution methods: Normalize and verify paths to prevent escaping the intended directory.
3. Restrict file access: Confirm that the resolved path is within the allowed base directory before accessing files.

Fixed Code Example

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

function readFile(filename) {
    // Fix: Sanitize and validate the filename to prevent path traversal
    const baseDirectory = '/var/www/uploads/';
    
    // Normalize the path to eliminate any traversal characters
    const safePath = path.normalize(path.join(baseDirectory, filename)); // Normalizes the path to prevent traversal
    
    // Ensure the resolved path starts with the base directory
    if (!safePath.startsWith(baseDirectory)) { // Check if the path is within the base directory
        throw new Error("Invalid file path");
    }
    
    return fs.readFileSync(safePath, 'utf8'); // Safe file access
}

// Example of safe usage
try {
    console.log(readFile("example.txt"));
} catch (error) {
    console.error(error.message);
}

These examples demonstrate the importance of input validation and path normalization to protect against path traversal vulnerabilities. Always ensure paths are safely constructed and validated against expected directory structures.