CWE-55: Path Equivalence: '/./' (Single Dot Directory)

What is Path Equivalence: '/./' (Single Dot Directory)?

• Overview: This vulnerability occurs when a software product incorrectly handles path inputs containing the '/./' sequence, which represents the current directory. Failure to validate or sanitize these inputs can lead to ambiguous path resolutions, allowing attackers to navigate the file system unexpectedly or access unauthorized files.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting '/./' into file paths to manipulate and traverse directories.
• Common attack patterns include directory traversal, where attackers aim to access files outside of the intended directory structure, potentially accessing sensitive information.

• Security Impact:

• Direct consequences include unauthorized file access, leading to potential disclosure of sensitive data.
• Potential cascading effects involve system compromise if critical configuration files or executables are accessed and manipulated.
• Business impact can range from data breaches, loss of customer trust, legal liabilities, and financial losses.

• Prevention Guidelines:

• Specific code-level fixes include validating and normalizing path inputs to remove '/./' sequences and ensure paths resolve correctly.
• Security best practices involve implementing stringent input validation and using parameterized file access methods to prevent path manipulation.
• Recommended tools and frameworks include utilizing security libraries that provide input sanitization functions and employing static analysis tools to detect path traversal 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 fs = require('fs');
const path = require('path');

function readFile(filePath) {
    // Vulnerable code: directly joins the user-provided file path
    // with the base directory without sanitization.
    // This allows an attacker to use '/./' or '../' to read unintended files.
    return fs.readFileSync(path.join('/var/www/data', filePath), 'utf8');
}

How to fix Path Equivalence: '/./' (Single Dot Directory)?

To fix this vulnerability, it's essential to sanitize and validate the file path to prevent directory traversal attacks. This involves normalizing the path to eliminate any '/./' sequences and ensuring the resolved path does not escape the intended directory. The following steps outline the process:

Steps to Fix:

1. Normalize the Path: Use path.normalize() to remove ambiguities such as '/./'.
2. Use Path Resolution: Use path.resolve() to convert the path to an absolute path and ensure it doesn't escape the intended directory.
3. Validate the Path: Verify that the resolved path starts with the designated base directory to prevent directory traversal.

Fixed Code Example

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

function readFile(filePath) {
    // Secure code: normalize and validate the path
    const baseDir = path.resolve('/var/www/data');
    const normalizedPath = path.normalize(filePath);
    const resolvedPath = path.resolve(baseDir, normalizedPath);

    // Ensure the resolved path is within the base directory
    if (!resolvedPath.startsWith(baseDir)) {
        throw new Error("Invalid file path: potential directory traversal attempt");
    }

    return fs.readFileSync(resolvedPath, 'utf8');
}

In both examples, the critical changes involve normalizing the path to remove '/./' and validating the path's location to prevent directory traversal. This ensures the application is protected against CWE-55 vulnerabilities by restricting file access to the intended directory.