XSS Vulnerabilities: What They Are and Why They Matter

Web applications exchange and store a lot of sensitive data, including emails, billing details, user personal information, and other information, which, if it falls into the hands of attackers, can threaten both website developers and users. Failing to set solid protection measures can result in data theft, monetary loss, compliance fines, and, most importantly, your company’s reputation.

One of the easiest ways for a user to be a victim of deceiving practices is via a cross-site scripting (XSS) attack. Let’s discover XSS vulnerabilities and how to secure your website from them.

What Are XSS Vulnerabilities?

Cross-site scripting vulnerability is a weakness of the web-based application that allows attackers to compromise client-side code. This happens when a person visits a website that has malicious code. Hackers usually send links, downloads, media content, or plugins, luring users to open and click on them. If the website doesn’t cover data sanitization and has XSS vulnerabilities, attackers gain access to the user’s personal information.

XSS Attacks: Prevalence and Potential Consequences

Cross-site scripting attacks are among the first in the ranking of high-risk attacks. Statistics claim that one in three websites is prone to being accessed by a hacker through malicious code injection and alteration. This is also because users might not recognize the suspicious link or web application and become victims. However, this doesn’t take responsibility from the developer’s side. If your website allows fraudulent code placement, then it is not secure.

XSS attacks do not always happen on the user’s side. They can damage the website by changing the content or inputting a redirect link that leads to a malicious website.

Being exposed to cross-site scripting vulnerabilities threatens with such consequences for website owners:

• Data leakage. When the user accesses a malicious link, the browser doesn’t recognize it and executes the script. Thus, all sensitive information, cookies, and session tokens are in danger of exposure.
• User capture. A successful XSS attack can result in gaining access to the user account. In this way, an “authorized” user who is an attacker can perform actions using session cookies.
• Reputational damage. Cross-site scripting vulnerabilities impact a company’s reputation. If a website defacement attack occurs, intruders can alter the content and misinform users. For governmental establishments, this can lead to inevitable consequences.

Script Threats with XSS Vulnerabilities Example

Script threats are malicious scripts attackers inject into websites. Inserting a script with altered code allows attackers to gain access to sensitive information and deface the platform.

Types of XSS Vulnerabilities

According to the Open Web Application Security Project (OWASP), three XSS attacks are reflected, stored, and DOM-based. Below are explanations for each.

Reflected XSS Attack

This common digital assault happens when the hacker sends malicious code to a vulnerable website. The browser processes the request and sends an HTTP response. The platform accepts the fraudulent code and makes it available for attackers to enter user-sensitive data and accounts. It is a non-persistent attack, meaning the invader sends the malicious code to every individual separately.

An example of a reflected XSS attack is the case in 2018 at British Airways. Customers were sent fraudulent URLs via advertisements and emails. They were tricked into clicking on them, and attackers gained access to billing data and other sensitive user information.

Stored XSS Attack

Stored or persistent attacks refer to the activity when hackers leave malicious code that remains in the system. So, every time the link or content is opened, it hijacks the viewer, providing access to session cookies and other information.

A real stored XSS attack occurred in 2010 on the Twitter social platform. The vulnerability was in the user’s ability to post JavaScript code in tweets. The group of hackers posted malicious content that compromised millions of users’ data and session cookies.

DOM-Based XSS Attack

The main target of the domain object model (DOM) XSS attack is the user’s browser. The attacks alter the DOM content and insert malicious URLs. After clicking on them, hackers gain access to user credentials, keystrokes, and other information.

This advanced and sophisticated XSS attack type occurred in 2019 in Adobe. The company allowed users to insert their code, which the attackers exploited. They inserted malicious JavaScript code; whenever someone clicked on it, the user could see fake error notifications or expose data.

The Role of User Input and Output in XSS Vulnerabilities

A similar aspect of most cross-site scripting attacks is the user input and output that trigger the malicious action. That is why controlling what information visitors enter is the first security measure for implementation. For example, if the field requires writing an email, the system should check if the “@” symbol is written.

Why Building XSS Attacks Resistant Website is Important

Cross-site scripting attacks affect many aspects of the website security. Failing to ensure the platform’s resistance to script threats can have the following results:

• User data stealing. By interacting with your web application, users entrust sensitive information that can be compromised during XSS attacks.
• Malware spreading. The website can become a fraudulent source that spreads malicious scripts if it is vulnerable to cross-site scripting.
• Trust and loyalty loss. One victim can be enough to build a notorious reputation for the brand.

Considering modern tendencies, XSS attacks are used for social engineering purposes like phishing. Such attacks are easy for a regular Internet user to get caught in just by clicking on a link that usually looks like a part of a trusted source.

How to Find XSS Vulnerabilities

Finding XSS vulnerabilities is done through website testing. This is how to apply test for XSS vulnerabilities to detect and fix weak security aspects of the application.

Conduct Manual and Automated Testing

Testing for XSS vulnerabilities can be executed manually or using automated tools. For manual methodology, quality assurance (QA) specialists explore input fields. This refers to checking every field in which the user writes the information, specifically fields that can process code.

Also, manual testing implies checking URLs to see if they resist malicious code being inserted by the attacker.

Testing XSS vulnerabilities in an automated way is done via scanning and analysis. Scanners can detect vulnerabilities according to the set requirements, and code analysis tools can investigate the source code for XSS weaknesses.

Choose Reliable Instruments

Automated instruments help identify issues quicker, leaving more time for fixing XSS vulnerabilities. When selecting the tool, QA teams evaluate the purpose of testing and the instrument’s capabilities since not every scanner is developed to prevent advanced attacks like DOM-based ones. Popular tools are OWASP ZAP, XSStrike, Burp Suite, and Acunetix.

To achieve the most efficient results, testers combine the best manual and automated testing practices and tailor the procedure to the specific project.

Preventing XSS Vulnerabilities

Cross-site scripting is an intricate attack that cannot be easily identified and fixed. These practices will help you secure your website from XSS attacks.

Input Sanitization

Greeting guests starts with learning more about them, which also applies to the digital sphere. To prevent hackers from inputting malicious data, follow a zero-trust approach and set a rigorous filtering system for any data input fields. Thus, before accepting the entered information, the website should validate it and only then process it.

Output Encoding

Ensuring the input data doesn’t contain suspicious information is not enough, as hackers can modify it. That is why output data encoding is needed. The rule is to display data exactly as the user typed it. Use HTML, JavaScript, CSS, URL encoding, or their combination.

Using Content Security Policy

Content security policy (CSP) is an additional layer of protection for preventing XSS attacks. Its mechanism restricts the processing of content that the website can load. CSP allows uploading only JavaScript files. However, it serves as a second-grade measure and doesn’t cover all external threats.

Final Words

Cross-site scripting vulnerabilities make the website easily accessible to attackers. The severe consequences the company can experience include enabling access to users’ sensitive information, spreading malware, and risking reputation. However, this can be prevented by implementing testing for XSS vulnerabilities.

Techniques like input sanitization, output encoding, allowing “secure” HTML only, and using a content security policy help reduce the potential risks of being hijacked via XSS attacks.

Professional QA teams can only conquer the complicated and sophisticated nature of cross-site scripting attacks. Experts at White Test Lab conduct a thorough examination of web applications so that the company doesn’t endanger XSS attacks. With us, you can ensure your platform is secure and thank yourself later!