CWE-1289: Improper Validation of Unsafe Equivalence in Input

What is Improper Validation of Unsafe Equivalence in Input?

• Overview: Improper Validation of Unsafe Equivalence in Input (CWE-1289) occurs when an application incorrectly determines that a potentially unsafe input is safe, especially when the input is used in operations like resource identification. This can lead to security vulnerabilities if the input is processed differently at a lower level or by another component.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting inputs that bypass validation checks but become dangerous when interpreted by downstream components.
• Common attack patterns include using variations in input case sensitivity, encoding, or similar representations to bypass filters.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access, data manipulation, or code execution (e.g., XSS).
• Potential cascading effects involve broader security breaches if the unsafe input affects multiple systems or components.
• Business impact may include data breaches, loss of customer trust, and financial losses due to the exploitation of vulnerabilities.

• Prevention Guidelines:

• Specific code-level fixes involve normalizing input data to a consistent state before validation and comparing against known safe patterns.
• Security best practices include implementing thorough input validation schemes and using whitelists instead of blacklists.
• Recommended tools and frameworks involve utilizing security libraries or frameworks that handle input validation robustly, such as OWASP's ESAPI or similar.

Corgea can automatically detect and fix Improper Validation of Unsafe Equivalence in Input in your codebase. Try Corgea free today.

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

const fs = require('fs');

function readUserFile(filename) {
    // Vulnerable to improper equivalence validation; allows unsafe file paths
    // This approach does not validate the input, potentially allowing directory traversal
    const filePath = `/user_data/\${filename}`;
    return fs.readFileSync(filePath, 'utf8');
}

How to fix Improper Validation of Unsafe Equivalence in Input?

To address this vulnerability in JavaScript, it's essential to validate and sanitize the input before using it in file paths or other critical operations. You should ensure that the input matches a specific pattern of allowed characters and does not include any sequences that can lead to directory traversal or other unsafe operations. Additionally, using path manipulation libraries can help ensure the safety of file paths.

Fixed Code Example

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

function readUserFile(filename) {
    // Validate that filename consists of valid characters only
    // This pattern allows alphanumeric characters, underscores, hyphens, and ends with .json
    if (!/^[\w-]+\.json\$/.test(filename)) {
        throw new Error("Invalid filename format. Only alphanumeric characters, underscores, hyphens, and .json extension are allowed.");
    }
    
    // Use path.join to safely concatenate file paths
    // This prevents directory traversal by normalizing the path
    const filePath = path.join(__dirname, 'user_data', filename);
    
    return fs.readFileSync(filePath, 'utf8');
}

In the JavaScript example, the key improvements include:

• Input Validation: The filename is checked against a strict regular expression pattern to ensure it only contains safe characters and ends with .json.
• Path Construction: Using path.join ensures that the file path is constructed safely, preventing directory traversal attacks by normalizing the path. This method combines the directory and filename in a way that inherently avoids unsafe paths.