Hardening jQuery: Essential Practices for Secure Applications

Hardening your jQuery implementation is crucial to protecting your application against common vulnerabilities like prototype pollution and cross-site scripting (XSS). By adopting robust security measures, you can fortify your application and ensure safer interactions for users. Below are key practices to strengthen your jQuery usage.

1- Protect Against Prototype Pollution

Prototype pollution is a critical vulnerability that allows attackers to manipulate the prototype chain, potentially altering application behavior. This risk is particularly prevalent in jQuery versions prior to 3.4.

Understand the Risk

Using functions like $.extend, properties such as __proto__ can be injected into objects, leading to unintended consequences:

var safe = {};
$.extend(true, safe, JSON.parse('{"__proto__": {"polluted": "yes"}}'));

console.log(safe.polluted); // undefined
console.log({}.polluted);   // "yes"

Mitigation Strategies

• Validate User Inputs: For JSON parse operations and other object manipulations, it is important to carefully validate the data coming from the user. Avoid adding properties such as __proto__, constructor, prototype.
• Freeze Objects: After rendering an object, you can use Object.freeze to make it unchangeable

const sanitizedObject = Object.freeze(sanitizeObject(userInput));

• Restrict Prototype Modifications: When creating objects, you can use the Object.defineProperty property to restrict the prototype chain so that default prototypes are not overwritten:

const obj = {};
Object.defineProperty(obj, "key", {
    value: "protectedValue", // The value of the property
    writable: false,        // Cannot be modified
    configurable: false     // Cannot be redefined
});

2- Avoid Cross-Site Scripting (XSS) Risks

XSS attacks can exploit improperly handled DOM manipulations in jQuery functions like .html() and .append().

// Data from user
const userInput = '<img src="x" onerror="alert(\'Hacked!\')" />';

// Dangerous usage
$('#content').html(userInput); 

Mitigation Strategies

• HTML Encode Input: If you are taking input from a user and reflecting it on your website, html encoding will be very useful.Html encoding converts special characters such as ?, &, /, <, > and spaces into their corresponding HTML or URL encoded equivalents.

const safeInput = htmlEncode(userInput);

• Implement Content Security Policy (CSP): Use and implement a CSP to disable all features that can be manipulated for an XSS attack.
• Understand Library Behavior: Read the documentation for the libraries referenced in your code to understand which elements allow embedded HTML.

3- Additional Security Recommendations

• Keep Your jQuery Version Up to Date.
• Using the .html() function in the Jquery library in versions below 3.5 is quite dangerous.
• If it is possible to freeze the prototype, this will increase your security.
• Pay extra attention to filtering when using the .append() function.
• jQuery functions like .append() and .html() manipulate the DOM directly and this can be abused.To add text, use the .text() function.
• Enable CSRF and CORS Controls.
• Event binding in jQuery (.on(), .bind()) can be abused and allow DOM manipulation.Use event delegation for event binding and focus on specific elements.
• Some plugins or functions in jQuery can indirectly trigger eval() or similar malicious functions.If you are using a third-party plugin, check the source code and be careful with eval() calls.

What is Jquery?

jQuery is a popular JavaScript library used to streamline web development processes. In particular, it enables common web development tasks such as navigating HTML documents, event handling, animations and AJAX operations with less code.

Features of jQuery:

• DOM Manipulation: jQuery provides easy access to the Document Object Model (DOM) of HTML pages and makes it possible to dynamically change the page content. For example, finding a specific element on a page and changing its style becomes very simple with jQuery.
• Event Processing: Easily capturing user interactions (clicks, mouse movements, keyboard presses, etc.) and defining actions to be taken as a result of these events is quite simple with jQuery.
• AJAX Support: jQuery offers the possibility to send AJAX requests to web pages and perform background server operations without reloading the page. This makes the page more dynamic and faster.
• Browser Compatibility: jQuery reduces compatibility issues between different web browsers. It has been widely used in the past to eliminate JavaScript incompatibilities due to browser differences.
• Animations: With jQuery it is very easy to add simple animations to page elements. For example, there are ready-made animation functions to slowly hide or make an element visible.
• Plugin Support: There are many plugins developed for jQuery. These plugins further extend the capabilities of jQuery, allowing to add advanced graphics, drag-and-drop functions, calendars and many more features.

Vulnerabilities Discovered in Jquery

• The highest vulnerable version at this time is 3.4.1. It is strongly recommended to use a version above this version (current version 3.7.1).
• You can go to the link to find out which vulnerabilities are in which version:
  https://www.cvedetails.com/version-list/6538/11031/1/Jquery-Jquery.html
• The presence of a vulnerability in a version does not necessarily mean that you will be affected by it even if you use the relevant version (this does not apply to all cases).This situation can be exemplified by a vulnerability in a function of any library of a programming language.You may not be using that function even if you use the library.
• A table of the types of vulnerabilities found in Jquery and their distribution over time: