Securing Websites Against XSS Attacks:
Must-Know for Developers and Site Owners

Cross Site Scripting (XSS) is a very serious kind of security issue saying that they target websites as well as the users who are using them. To put it simply, XSS attacks means that a hacker was able to inject malicious scripts into a website. These scripts would then run in the user's browser, many a time without the user knowing about it. Most commonly, these attacks are aimed at stealing some sensitive information, impersonating the user, or just playing around with how the website looks or behaves. Cross site scripting is, therefore, a very necessary understanding that any website owner or developer or even the person who just likes shopping or browsing on the internet needs to have.

Just when you are shopping on a retail site, a pop-up suddenly appears redirecting you to another website without clicking anything. How did this happen? It's that simple-it's an example of XSS attacks. A couple of years back, just during the holidays, a popular retail site was under an XSS attack. Hackers injected malicious codes into product reviews. Whenever another user visited these reviews, the codes would automatically be executed in their browsers, collecting user’s personal data from cookies. The result? Not just financial losses to the company, but loss of customers too.

XSS attack refers to an injected malicious script into a web application client, often through user input and executed in the browser while the actual user is visiting the page. Common outcomes include personal data theft, impersonation of a legitimate user, and alteration of a website's appearance and behavior. It probably originated in the '90s and led to a lot of XSS vulnerabilities. Subsequently, in this evolving era of the internet, cross site scripting has entered every field of concern for companies and even end users, despite having one of the greatest advancements in web security regarding attacks.

Imagine the scenario: you’re searching on a site. This site does not properly sanitize the input, which means it does not care about the data you enter in terms of maliciousness. An attacker may use this. For instance, creating a link that goes like the example given below:

Different forms of XSS attacks exist. Here is a quick overview of the most usually practiced types:

1.Reflected XSS Attack:

What does it refer to: In Reflected XSS, the injected script by the attacker is immediately reflected off the web server itself and gets executed in the user's browser. Sometimes, the user input such as query parameters or form input is reflected on the page without any kind of sanitization or escaping.

For example, a website where users get to search for products. The search term gets into the content of the page directly without any kind of sanitization.

• Consider a URL including user’s name as a query parameter having profile?name=[maliciousinput]

If a user clicks on this link, then the attacker's script will get executed in the browser of a victim, causing alert box to pop-up. Though this is a very straightforward example, an attacker would be able to take advantage of this occurrence, for example, to steal an entire session cookie or any sensitive data.

Real-world instance: A common example of reflected XSS would be seen in searching forms when the input of the user would have been displayed on the page without sanitization. If someone creates a malicious URL that contains a malicious script, the user can even be tricked into running the script.

2. Stored XSS Cross Site Scripting Attack (Persistent XSS Attacks)

What does it refer to: Stored XSS attack, also called persistent XSS attack is a type of cross scripting attack that happens when the malicious payload of the attacker is not saved permanently on the target server but in a database or any other persistent storage. This means that the attacker thinks his payload runs every time a user accesses the compromised website.

Example: Imagine a blog where users can post comments on articles. If that website does not sanitize input from users properly, then someone can alter comments with embedded JavaScript.

• Malicious Comment: After the comment has been submitted, it is kept on the server. Whenever a user views the blog post, that script in the comment gets executed in their browser.

Real-World Scenario: A good instance of stored XSS vulnerability would be such as when the attackers injected JavaScript around the areas of comments within several sites. Other users viewed these comments, and the script executes within their browsers, stealing their login credentials or session cookies.

3. DOM-based XSS Attack

What does it refer to: DOM-based XSS vulnerability is the nature of a client-side attack, where the vulnerability lies in the client-side coding (Java-Script) rather than the server-side. This kind of attack does not communicate with the server but just modifies the DOM, Document Object Model of the page, and executes the script.

For example, a website that allows providing input via URL query string takes that input using JavaScript and displays it on the page. If this input is directly inserted into the page without being sanitized through the website JavaScript code, then the script from the URL will execute, constituting an example of DOM-based XSS vulnerability where the attack only happens on the client side.

Real-World Scenario: An example of DOM-based cross scripting attack is when user directly inputs to the page using JavaScript. A webpage takes input from the URL parameters and shows the user's name in the title tag or somewhere else using that input. If the input isn't sanitized in the JavaScript code, the attacker can even exploit this malicious payload through the URL.

Each type of XSS vulnerability can be significant for security breaches, so it’s essential to use proper security practices such as input validation, output encoding, and implementing Content Security Policies (CSP) to mitigate the risk of cross site scripting attack.

There are plenty of ways to detect and protect against cross site scripting. Here are some ways listed below:

• Automated Tools That Security Scans: With the different kinds of XSS scanners available, one will be able to detect XSS vulnerability from the codes existing on one's website.
• Manual Testing: Manual tests including those involving penetration testing by security experts are other options for finding hidden vulnerabilities.
• Code Reviews at Regular Intervals: Your team needs to review the source code of the website at regular intervals to look for the additional signs of possible security weaknesses, especially when it concerns user input.
• Security Header: There are chances of reducing the risk of XSS attacks. This can be done by implementing Content-Security-Policy (CSP) as security protective headers to restrict what scripts can run on your site.
• Input Sanitization: Validating and sanitizing user inputs will always prove that there are no harmful scripts getting through.
• Output Encoding: This message states that encoding output is just as important as input. Even if malicious code crosses through, it will not execute in the browser.
• Use Secure Libraries and Frameworks: Much modern libraries and frameworks really make it more straightforward to avoid XSS attack since they have built-in protections that make XSS vulnerability less chances of occurrence.

These steps will help in securing the website against any risks to the actions getting taken in case of an XSS attacks.

Cross Site Scripting or XSS attacks are one of the common methods for attackers to steal cookies from users. Cookies contain session tokens, and their authentication details, which make them easy targets. If an attacker successfully steals these cookies, then the attacker can log into the user's session and impersonate the user with access to sensitive information or capability of malicious activity.

Assume a website where users log in and browse around content by posting comments on articles. This site stores a user's authentication data in cookies so that a user could stay logged in. Unfortunately, the website is vulnerable through the comment section of its pages due to improper sanitization of user input, thus allowing any XSS attack.

Attack Breakdown:

• Injection of malicious code: The attacker finds an XSS vulnerability in the comment section and then posts the following comment with malicious JavaScript code. Like the script reads document. Cookie and sends the data to a remote URL using a fetch () request. The victim's cookies are captured and sent to the attacker's server.
• Store Malicious Comment: The website does not sanitize the input; hence the malicious comment remains stored in the database. The script would run in the browser every time the comment was viewed.
• Victim Loads the Page: A legitimate user visits the website and while viewing the comments, malicious script executes automatically in the comment given by the attacker.
• Cookies Are Stolen: The malicious script sends the cookies of legitimate user to the attacker. These cookies could hold sensitive information like session tokens or credentials for authentication.
• Access Granted to the Attacker: The attacker now has the cookies of the original user, with which he can impersonate the victim. This access to the victim's account and sensitive information allows the attacker to carry out activities such as conducting purchases or stealing personal information.

Impact:

• Account Hijacking: The attacker impersonates the victim, accesses his account, and acts maliciously.
• Data Breach: Sensitive data gets compromised, such as user's identity and financial information.
• Reputation Damage: Users lose trust on the website, and that leads to the damaged reputation.

Consider the following instances of XSS (Cross Site Scripting) attack using various HTML tags.

1. Script Tag XSS Attack: This is the most common cross site scripting attack, where the page is compromised through the injection of malicious JavaScript codes.

Example: A script that shows a popup message using JavaScript’s alert () function.

• How It Works: The attacker injects a script tag through some input form, URL, or comment section. On loading the page by other users, the script gets executed, and an alert message is displayed (or some more malicious actions are executed).

2. Image Tag (Using the onerror Attribute): An attacker can inject JavaScript into HTML tags like using the onerror event to execute code when the image fails to load.

Example: The attacker provides an image tag with an invalid src URL. When the image cannot load, the onerror event triggers and executes the malicious JavaScript.

• How It Works: The attacker provides an image tag with an invalid src URL. When the image cannot load, the onerror event triggers and executes the malicious JavaScript.

3. Anchor Tag XSS Attack (Using href and javascript): An attacker can insert JavaScript code into the href attribute of a link.

• How It Works: The attacker creates a link with a javascript: protocol in the href attribute. Upon clicking the link, the malicious script will be executed.

4. Input Field Cross Site Vulnerability (Using onfocus or onblur Events): JavaScript can be triggered from various events in form fields onfocus, onblur etc.

• How It Works: This input field is injected into a form by the attacker. When a user clicks into the input field (focus), the script runs to alert.

5. Iframe Tag XSS Vulnerability: An attacker can inject an iframe tag with a malicious source, embedding a harmful page or script into the target website.

• How It Works: This malicious iframe attempts to load a JavaScript payload on page load. If the target site allows iframe embedding without any filtering, further malicious actions can be taken.

6. Meta Tag Cross Site Scripting Attack (Using http-equiv and content attributes): Operating via tags for redirection or content injection is one kind of XSS attack.

• How It Works: The attacker injects a meta tag to redirect users to a malicious script immediately.

7. Style Tag XSS attack (Using background in CSS): Malicious scripts can be executed via CSS properties such as background or url().

• How It Works: The attacker injects a CSS background property with a JavaScript: URL that will cause the script to execute upon rendering of the page.

8. Audio/Video Tag XSS vulnerability (Using onplay or onload Attributes): Audio and video elements can also be used for executing scripts when certain events like onplay or onload are triggered.

• How It Works: The attacker can inject an audio tag with the onplay event. Upon playing the audio by the victim, the malicious script gets triggered.

9. Form Submission XSS attack (Using action Attribute): An attacker can manipulate a form so that when it is submitted, JavaScript is executed rather than the form data being submitted.

• How It Works: The attacker builds a form that has an action set to malicious script. When the user submits the form, the script runs instead of sending its data.

10. SVG Tag Cross Site Scripting Attack: SVG (Scalable Vector Graphics) elements can also be exploited to execute JavaScript.

• How It Works: The attacker injects an SVG tag with an onload event that triggers the script when the SVG image is loaded.

The real consequence of XSS vulnerabilities

The risk is great. Among many others, here are some risks associated with XSS vulnerabilities harming users and organizations:

• Data Theft: The hacker can now steal all sensitive information, even session cookies or login credentials, allowing him to impersonate the user and access the account.
• Website Manipulation: A malicious script could manipulate the website content-hack has posted false information in comments or reviews, even changing prices in an online store.
• Malware Delivery: An XSS vulnerability can deliver malware to the user's computer, leading to other attacks.
• The Damage: Apart from the damage of compromise, there are costs involved in cleanup and reputation loss faced by the company along with fines should any sensitive customer data get exposed (like under GDPR).

Conclusion

Cross Site Scripting (XSS) attacks come at the center of the greatest threats to the integrity of a website and the sensitive information stored over it by its users. Manipulating different HTML tags, such as script, img and anchor tag among others, an attacker can have scripts loaded as a malicious code that steals cookies, hijacks sessions, or performs other cataclysmic consequences. These attacks indicate a phenomenon that emphasizes the critical importance of input and output for web applications from completion.

There is a need to observe preventive measures against XSS attacks, which will also entail making the following recommendation practices by developers, which include input sanitizing, output encoding, setting cookie flags as an effective HttpOnly, Secure, and implementing Content Security Policy (CSP).

Understanding all the possible ways of conducting such an attack, along with supporting robust security measures, thereby helping protect the business website from threat actors abusing the discoveries made from such vulnerability.