![]() ![]() On the client side, the HTTP response does not change but the script executes in malicious manner. DOM-based cross-site scripting attackĭOM-based XSS is also sometimes called “type-0 XSS.” It occurs when the XSS vector executes as a result of a DOM modification on a website in a user’s browser. Google’s orkut was vulnerable to persistent XSS that ruined the reputation of the website. Persistent XSS is more harmful that non-persistent XSS, because the script will automatically execute whenever the user opens the page to see the content. In the above examples, the second example of messaging a website was a persistent XSS attack. Every time the user opens the browser, the script executes. It occurs when XSS vectors are stored in the website database and executed when a page is opened by the user. Persistent cross-site scripting is also known as stored cross-site scripting. A typical non-persistent XSS contains a link with XSS vector. If you take a look at the examples we have shown above, the first XSS example was a non-persistent attack. In this, data injected by attacker is reflected in the response. Non-persistent XSS is also known as reflected cross-site vulnerability. Non-persistent cross-site scripting attack There is no standard classification, but most of the experts classify XSS in these three flavors: non-persistent XSS, persistent XSS, and DOM-based XSS. With a valid session id, the attacker can hijack the other person’s account. When the other person tries to read the message, the cookie-stealing script will be executed and his session id is now on the attacker’s side. This script will be stored on the website as a message. Suppose an attacker has sent some cookie-stealing script in the message. Another person will see the message when he opens the message from the inbox. When this form is submitted, the message will be stored in the database. A basic form will look something like this: In this website, users can send messages to their contacts. Suppose there is a website with a messaging feature. It will be executed by the browser and it will display an alert box saying “XSS injection.” Example 2 ![]() So, at the keyword place, it will look like this: If web application has nothing implemented to encode input and filter malicious scripts, it will take input as it is and then print on webpage where it will be called. Now think what happens if an attacker tries to inject malicious script from this side. Whatever a person searches for, it will be displayed on the web page along with search results. On web pages, it is generally coded like this: On the search.php page where it shows search results, it also lists the search keyword in the form of “Search results for Keyword” or “You Searched for Keyword.” This search form looks something like this With this search box, you can search to find anything available on the website. You see a search box on almost all websites. Most of the times, XSS is used to steal cookies and steal session tokens of a valid user to perform session hijacking. When the browser executes the script, a malicious action is performed on the client side. And a browser has no way to know that it should not trust a script. If the input is not properly encoded and sanitized, this injected malicious script will be sent to users. This flaw can be found anywhere in an application where user input has been taken but not properly encoded. A cross-site scripting attack occurs when a web application executes a script that the attacker supplied to end users. So cross-site scripting is called XSS so it does not get confused with CSS. In web design, we have cascading style sheet s (CSS). The first question that comes in mind is why we call it “XSS” instead of “CSS.” The answer is simple and known to all who work in web development. Cross-site scripting is also known as an XSS attack. ![]() In cross-site scripting, malicious code executes on the browser side and affects users. What Is cross-site scripting?Ī cross-site scripting attack is a kind of attack on web applications in which attackers try to inject malicious scripts to perform malicious actions on trusted websites. We will also see few open source libraries that will help you in patching Cross-site Script vulnerability in your web application. In this post, we will see what a cross-site scripting attack is and how to create a filter to prevent it. ![]()
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