Xss what can you do

And this worked, the site just checks once if the payload contains the script tags and removes them, once it removes them we get another set of script tags that we wrapped around the removed ones and we get the successful alert prompt.

Injecting a basic a tag and seeing how the site reacts to that. What we do here is basically create a link that says click me, and when we hover the mouse over it, the alert box should execute. And that worked because the whole focus of filtering was the script tag, the developers forgot about a tag and left that for the injections. Open up your developer tools by pressing F12 in your favorite browser and go to the Console tab.

Type the following String. You should get the character a displayed in your console. Function is String. This is the standard way of working through to figure out how to get the prompt to appear, iteratively trying things until something sticks and then modifying the thing that sticks the best to get the prompt.

Another good thing to do is to inspect the element and see the code around it to see if you can get something out of that. The site we used to test these injections is Broken Crystals , and you can also contribute to it to make it better.

XSS Payloads can and do get really crazy real fast, and the AppSec community created some great payloads that you can just copy and paste to see if they work. Polyglots are used to save time when testing for XSS. They usually cover a large variety of injection contexts. It all depends on your goal, if it is to test a lot of parameters, polyglots are great, if it is to break a single parameter, you will probably need to dig deep into how that specific part of the application works.

Here is a great polyglot by 0xSobky. It covers a large amount of injection contexts and is overall great polyglot to test everything with. Another great polyglot by s0md3v. You can find many other polyglots here. And once we probe it a bit we find out that we can change the password without supplying the old password.

So we wrap with iframe and send a proper HttpRequest to get this to work like. And now we can send this link to our target and their password will be changed to whatever you put there. It reflects the pack on the page. Now anyone that visits our profile gets popup. You will get the popup. Reflected and stored cross-site scripting can be sanitized on the server-side and there are multiple ways of doing it. One great way to start is to use a security encoding library to encode all parameters and user input.

What you need to do is whitelist what is allowed. Frequently asked questions How does Cross-site Scripting work? Note that about one in three websites is vulnerable to Cross-site scripting. Learn more about the current state of web security.

For example, an attacker may use it to steal user credentials and log in to your website as that user. If that user is an administrator, the attacker gains control over your website. See an example of a dangerous XSS attack from the past. To discover Cross-site Scripting, you may either perform manual penetration testing or first use a vulnerability scanner. If you use a vulnerability scanner, it will save you a lot of time and money because your penetration testers can then focus on more challenging vulnerabilities.

To protect against Cross-site Scripting, you must scan your website or web application regularly or at least after every chance in the code. Then, your developers must correct the code to eliminate the vulnerability.

Contrary to popular opinions, web application firewalls do not protect against Cross-site Scripting, they just make the attack more difficult — the vulnerability is still there.

See what Acunetix Premium can do for you. However, JavaScript can still be dangerous if misused as part of malicious content: Malicious JavaScript has access to all the objects that the rest of the web page has access to. Cookies are often used to store session tokens.

JavaScript can read the browser DOM and make arbitrary modifications to it. Luckily, this is only possible within the page where JavaScript is running. Most of these APIs require user opt-in, but the attacker can use social engineering to go around that limitation.

After that, the victim must visit the web page with the malicious code. The victim requests the web page from the web server. Cross-site Scripting Attack Vectors The following is a list of common XSS attack vectors that an attacker could use to compromise the security of a website or web application through an XSS attack.

Step 1: Train and maintain awareness To keep your web application safe, everyone involved in building the web application must be aware of the risks associated with XSS vulnerabilities. How does Cross-site Scripting work?

Why is Cross-site Scripting dangerous? When successful, they make the user's browser execute an arbitrary script on a given page. The same-origin policy is supposed to allow scripts only when a script is loaded from the same domain as the page that the user is currently viewing.

And in reality, attackers don't have direct access to the server responsible for the page displayed by the browser. So how do attackers do it? Application vulnerabilities can help attackers by enabling them to embed fragments and malicious code in page content. For example, a typical search engine echoes the user's query when displaying search results.

Will the contents of the search results page lead to this script being executed, and will a dialog box with the message "1" appear? This depends on how well the web application developers verify user input and transform it into a safe format. The main difficulty lies in the fact that users run a wide variety of browser versions, from the latest pre-alphas to ones that are no longer supported.

Every browser handles web pages in a slightly different way. In some cases, an XSS attack can be quite successful when inputs are not sufficiently filtered.

So the first step in an XSS attack is to determine how to embed user data on a web page. The second step is for the attacker to convince the user to visit a specific page. The attacker also needs to pass the attack vector to the page. Once again, there is nothing here that poses a serious obstacle. Websites often accept data as part of a URL. To implement the attack vector, attackers can use various social engineering or phishing methods.

The following example code displays just such a string passed by the user in the HTTP request in the server's response:. The code processes the value of the first URL parameter passed in the user's request.

Then it displays the parameter on the resulting web page. The developer seemingly doesn't expect to see anything other than plain text without HTML tags in the firstName parameter. You can easily check that when this HTML fragment is loaded onto a web page in the user's browser, the script passed in the firstName URL parameter is executed.

In this case, malicious JavaScript is executed in the context of the vulnerable server. The script can therefore access the domain's cookie data, its API, and more. Of course, the attacker will develop the actual vector in a way that conceals their presence on the user-viewed page.

According to Positive Technologies analytics , XSS is among the three most common web application attacks. The relative percentage of XSS compared to other attack types has dipped in previous years. Still, there is no sign of XSS losing popularity. Why is XSS still near the top of the list? Consider the number of vulnerable websites. As detailed in our report , more than two-thirds of tested websites had XSS vulnerabilities. If the server's request and response are semantically related, the server's response is formed from the request data.

For example, the request could be a search query and the response might be the results page. In this case, the page as displayed on the server side will cause JavaScript to be executed in the context of the server, which is part of the original attack vector. This type of application vulnerability occurs when a attack vector contains JavaScript that doesn't come in a user request. Instead, the JavaScript code is downloaded from the server such as the database or file system.

The application might allow you to save data from an untrusted source and, subsequently, use this data to generate a server response to a client's request. Imagine an online forum where people communicate regularly.

If the application is vulnerable, an attacker can post a message with embedded JavaScript. The message will be saved in the system database. After that, the script in question will be executed by all users who read the message posted by the attacker. Here, data is read from the database and the results are passed along without client verification. If the data stored in the database contains HTML escape sequences, including JavaScript, the data will be passed to the client and executed by the browser in the context of the web application.

The two types of XSS vulnerabilities described above have something in common: the web page with embedded JavaScript is formed on the server side. However, the client frameworks used in modern web applications allow changing a web page without accessing the server. The document object model can be modified directly on the client side. The main premise behind this vulnerability remains the same: specifically, poorly implemented processing of HTML escape sequences.

This leads to attacker-controlled JavaScript appearing in the text of a web page. Then this code is executed in the server context. The HTML code has an element with the "message-text" identifier, meaning that it is used to display the text of a message. The script displays the message with the html function, which doesn't sanitize HTML escape sequences.

Therefore, such an implementation is vulnerable. For example, the following could be passed to this function:. Before we go into specific examples, we should also point out an important distinction.

Some XSS attacks are aimed at acquiring information only once. In these cases, the victim computer executes a malicious script and sends stolen information to an attacker-controlled server. The primary goal of an XSS attack is to access the user's resources. Let's look at a few examples of such attacks. Imagine the following scenario. A user opens a browser and goes to an online banking page. The user is prompted to log in with their username and password.

Obviously, the user's subsequent actions should then be regarded as legitimate. But how do you verify this legitimacy without asking the user to log in after every single click? Fortunately for users, there is a way of doing that. After successful authentication, the server generates a string that uniquely identifies the current user session. This string is passed in a response header, in the form of cookie data.

On subsequent visits to the server, the cookie data will be automatically included in the request. This data will be used by the server to determine whether the request comes from a legitimate user. Naturally, the security of session cookies then becomes critical. Any interception of this information would enable impersonating a legitimate user. One of the classic ways to transfer session cookie data to an attacker is to send an HTTP request from the user's web browser to an attacker-controlled server.

In this case, the request is generated by JavaScript that is embedded on a vulnerable web page. The cookie data is then transmitted in the parameters of this request. One example of an attack vector could be the following:. In this example, the user's web browser creates an image object in the DOM model. After that, it tries to load the image from the address specified in the src tag.

The browser then sends the cookie data to the attacker's site with the corresponding HTTP request handler:. In this case, an attacker only needs to listen to incoming connections, or else configure event logs and obtain cookie data from the log files this is described later in more detail.

JavaScript is a very capable programming language. An attacker can use these abilities, combined with XSS vulnerabilities, simultaneously as part of an attack vector. So instead of XSS being a way just to obtain critical user data, it can also be a way to conduct an attack directly from the user's browser.

These requests can be used to send comments or to conduct financial transactions:. By exploiting an XSS vulnerability with this attack vector, malicious actors can transfer any specified amount of money to their accounts. This allows an attacker to change how the website appears to the user, such as by creating fake input forms. If a vulnerable web application permits modifications to the DOM model, an attacker could inject a fake authentication form into the web page by using the following attack vector:.

Any credentials that a user enters in this form will be sent as a POST request to the evil.