CWE-83: Improper Neutralization of Script in Attributes in a Web Page

What is Improper Neutralization of Script in Attributes in a Web Page?

• Overview: This vulnerability involves failing to properly handle or sanitize script content within HTML attributes on a web page, which can allow attackers to inject malicious scripts. These scripts can execute within the context of the user's browser, potentially leading to unauthorized actions.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting JavaScript or other malicious code into attributes of HTML tags, such as onmouseover, onload, onerror, or style.
• Common attack patterns include using specially crafted input that includes JavaScript URIs or other script-based payloads to trigger unintended script execution.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized script execution, which can lead to data theft, session hijacking, or defacement of the website.
• Potential cascading effects might include further exploitation of the user's session or spreading malware to other users.
• Business impact could involve loss of customer trust, legal ramifications, and damage to brand reputation due to data breaches or other malicious activities.

• Prevention Guidelines:

• Specific code-level fixes involve properly escaping or encoding input data before inserting it into HTML attributes, ensuring that any script content is neutralized.
• Security best practices include validating and sanitizing all user inputs, using content security policies (CSP), and avoiding inline scripts or event handlers where possible.
• Recommended tools and frameworks include using libraries and frameworks that automatically handle input sanitization, such as OWASP's Java Encoder or similar utilities in modern web frameworks.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

JavaScript Example

// Example of a function that generates an HTML element with user-provided data
function generateUserProfileLink(userName) {
    // Vulnerable to XSS: Improper neutralization of the `href` attribute
    return `<a href="javascript:alert('Hello, \${userName}!')">Click here to greet</a>`;
}

// Usage example
document.body.innerHTML = generateUserProfileLink("User"); // User input is directly injected

Explanation:

• Vulnerability: The generateUserProfileLink function constructs an anchor (<a>) element with a javascript: URI in the href attribute. The userName is directly inserted into the URI without any neutralization, allowing execution of arbitrary JavaScript if userName is controlled by an attacker. This is a classic Cross-Site Scripting (XSS) vulnerability.

How to fix Improper Neutralization of Script in Attributes in a Web Page?

To mitigate this vulnerability, avoid using javascript: URIs entirely in attributes such as href. Instead, use safer event handling approaches. Here's how you can fix it:

1. Avoid javascript: URIs: Do not use javascript: in HTML attributes. This is a common source of XSS vulnerabilities.
2. Use Event Listeners: Use event listeners to handle JavaScript actions rather than embedding them in href or on* attributes.
3. Sanitize Inputs: Sanitize user inputs to ensure that they do not contain dangerous characters or scripts.

Fixed Code Example

// Secure function that generates an HTML element with user-provided data
function generateUserProfileLink(userName) {
    // Create an anchor element safely
    const anchor = document.createElement('a');
    anchor.textContent = 'Click here to greet';
    anchor.href = '#'; // Use a benign href value
    // Use a click event listener for handling actions
    anchor.addEventListener('click', function(event) {
        event.preventDefault(); // Prevent default anchor behavior
        alert(`Hello, \${userName}!`); // Safe use of user input
    });
    return anchor.outerHTML;
}

// Usage example
document.body.innerHTML = generateUserProfileLink("User");

Explanation:

• Fixed Code:
  • We create an anchor element using document.createElement('a') and set its textContent and href attributes to safe values.
  • Instead of embedding JavaScript directly in the href, we add an event listener for the click event to handle actions.
  • This approach ensures that any action performed is controlled and does not expose the application to XSS attacks.
• Security Controls:
  • Event Listeners: Use event listeners as a best practice for handling JavaScript actions.
  • Input Handling: Although not directly sanitized here, the input is used in a controlled context where its manipulation cannot lead to script execution.