DOM-Based XSS

DOM-based cross-site scripting (XSS) is a type of cross-site scripting vulnerability that occurs when a web application's client-side script in the Document Object Model (DOM) is used to execute malicious code in a user's web browser. This can happen when a web application does not properly validate user input or fails to properly encode output.

This vulnerability occurs when a web application allows users to search for products and displays the search results in the browser. If the application does not properly validate user input, an attacker could craft a search query that includes malicious code, such as a script, and then embed that script in the search results page. When the results are displayed in the browser, the script will execute in the user's web browser and can steal sensitive information, such as session cookies, or perform other malicious actions.

For example, imagine a web application that allows users to search for products and displays the results in the browser. The application does not properly validate the user's input and the attacker crafts a search query with a script like this: http://example.com/search?q= When the user clicks on the link, the script is executed and an alert box is displayed with the user's session cookie, which can be used by the attacker to hijack the user's session.

This example illustrates how a DOM-based XSS vulnerability can occur when a web application does not properly validate user input. It highlights the importance of properly validating and sanitizing user input, and properly encoding output before it is rendered in the browser, to prevent such attacks.

In August 2016, a security researcher discovered a DOM-based XSS vulnerability on the popular social media platform, Instagram. The vulnerability was caused by Instagram's use of a single JavaScript file to handle all of the user input on the website. The researcher found that by manipulating the URL, he could inject malicious JavaScript into the page, which would then execute in the victim's browser. Instagram has since fixed the vulnerability, however it serves as a real-life example of how a DOM-based XSS attack can occur and the potential impact it can have.

Burp Suite is a web application security testing tool that can be used to identify potential DOM-based XSS vulnerabilities in web applications. It allows you to intercept and manipulate requests and responses, and it has a built-in scanner to detect different types of vulnerabilities. OWASP ZAP, a web application security scanner can be used to identify potential vulnerabilities in web applications, including DOM-based XSS vulnerabilities. It also allows intercepting and manipulating requests and responses.

Nessus (a vulnerability scanner can be used to identify potential vulnerabilities in networks and systems, including those related to DOM-based XSS), Acunetix (a web application security scanner can detect DOM-based XSS vulnerabilities, as well as other types of vulnerabilities), WebInspect (also a web application security scanner can detect DOM-based XSS vulnerabilities, as well as other types of vulnerabilities), W3af (an open-source web application security scanner that can detect DOM-based XSS vulnerabilities, as well as other types of vulnerabilities), Sqlmap (a tool that automates the detection and exploitation of SQL injection vulnerabilities and has an option to check for DOM-based XSS vulnerabilities) are tool that can be used to detect potential DOM-based XSS vulnerabilities. Although they detect these vulnerabilities, they do not replace manual testing and review by a security professional.

DOM-based cross-site scripting (XSS) vulnerabilities can give rise to some risks which are;

Account takeover: Here, an attacker can use a DOM-based XSS vulnerability to steal a user's session cookies, which can be used to take over the user's account and gain access to sensitive information or the ability to perform unauthorized actions.

Financial loss: An attacker can use a DOM-based XSS vulnerability to steal sensitive information, such as financial data, or perform financial transactions, such as unauthorized purchases. Data leakage: An attacker can use a DOM-based XSS vulnerability to steal sensitive information, such as personal or financial data.

Reputation damage: If an attacker is able to use a DOM-based XSS vulnerability to steal sensitive information or perform unauthorized actions on a user's behalf, it can lead to damage to the organization's reputation and loss of trust from customers. Compliance violation: A DOM-based XSS vulnerability can lead to a violation of compliance regulations, such as those related to data privacy or financial transactions.

Amplification of attacks: A DOM-based XSS vulnerability can be used to amplify the impact of other attacks, such as phishing or malware.

Spread of malware: A DOM-based XSS vulnerability can also be used to spread malware, by injecting malicious code into the web page and tricking the user into downloading and installing malware from the website.

It's crucial for organizations to identify and fix DOM-based XSS vulnerabilities in their web applications to protect users and organizations from these risks listed above.