Cross-Site Scripting (XSS): What Is It and Why Is It Dangerous?

cross-site scripting
Cross-Site Scripting

Internet users are constantly exposed to cross-site scripting (XSS) attacks daily. As a result, users can be impersonated, private information can be stolen, websites can be defaced, and many other things can happen. 

Having said that, what does a cross-site scripting attack mean? Is it a security threat? If so, why? How can you protect your website against cross-site scripting attacks?

What is Cross-Site Scripting?

prevent cross site scripting attacks

In the world of web application security, Cross-Site Scripting (or XSS for short) is a vulnerability that allows attackers to inject arbitrary codes or scripts into webpages due to cross-site scripting vulnerabilities.

An unsuspecting user may interact with an infected web page, triggering the injected code. The victim could be hit by an attack that has the capability of stealing sensitive information or allowing the attacker to conduct unsolicited transactions on their behalf.

Malicious scripts can masquerade as legitimate users on a website to steal information from them, steal cookies, manipulate the site’s content, deface the site, and redirect users to websites that contain malware.

There is no doubt that XSS attacks are nothing new. Over 274,000 reported occurrences of these attacks since they first surfaced in the 1990s, with more than 274,000 reported occurrences in 2021 alone. XSS has consistently been listed by the Open Web Application Security Project (OWASP) as one of the top 10 web security risks.  

How Does XSS Work?

Websites that fail to secure input data are vulnerable to XSS attacks. HTML content is not adequately extracted from input by the website.

Why is this a bad thing? Your web browser can’t differentiate between your website’s original code and the code injected into it. If an attacker were to inject malicious scripts (JavaScript, VBScript, etc.) into the site’s code, then it would pass it off as valid input, and thus the attacker would be able to cause the website to crash.

Attacks by cross-site scripting include the following types:

As a result of the execution and delivery of the script, cross-site scripting attacks (XSS) can be classified into three different types, as follows: 

Reflected Cross-Site Scripting (XSS)

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Reflected cross-site scripting occurs when the code injected into a web server responds with the input data as part of the request sent to the server. In this case, the injected code is reflected off the web server. 

The browser executes the script based on the input validation performed incorrectly, and it returns the client the hand output.

Stored Cross-Site Scripting (XSS)

xss attacks: what is cross-site scripting and why is it a security risk? evalian®

The term “stored cross-site scripting” describes a type of XSS attack in which malicious code is inserted or stored in an application’s database that is maintained on a web server. 

There is no doubt that this is the deadliest type of XSS attack because it can potentially compromise the security of the entire website’s user base. As a result, users who visit a website embedded with malicious code will be hit by the payload as soon as they see the page.

DOM-Based Cross-Site Scripting (XSS)

dom based


An attack targeted toward DOMs using cross-site scripting (XSS) is known as DOM-based cross-site scripting (XSS). It involves the injection of malicious code into the DOM of the browser and then executing it by the browser as the attack proceeds. There is a chance of this happening due to the website’s inability to sanitize the input correctly.

Using a script, an attacker can access the DOM and manipulate its content in a vulnerable web application. It is also relevant to note that DOM-based XSS is also delivered via social engineering, just as it is with reflected XSS. This exploit involves tricking the victim into clicking a malicious URL. This leads them to the vulnerable page, where the browser executes the script as soon as the victim clicks the URL.

What are the best ways to detect and prevent XSS vulnerabilities on your website?

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There are several reasons why cross-site scripting (XSS) vulnerabilities are still as prevalent today as they were decades ago. One of the main reasons is that they are challenging to detect and patch. As a result, ensuring your website follows the best development practices and prioritizing security can help you avoid cyberattacks and breaches that can cause you money.

The following tips can assist developers in preventing XSS attacks in the future:

  • As a general rule, do not rely on user input as a source of information. XSS attacks can be carried out on any user input rendered in the HTML as part of the page.
  • Ensure that all scripts fed into input fields are properly escaped by encoding or running techniques.
  • Remove any injected scripts from the user input by sanitizing the input.
  • It is possible to make cookies inaccessible to client-side scripting by setting the HttpOnly flag.
  • Ensure that the Content Security Policy (CSP) is enforced so that scripts that have not been authenticated are not injected into the web page.

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Moreover, it is also vital that you remain vigilant when it comes to clicking on links and visiting websites.