09 Jan, 2023

XSS

Vulnerability Assessment as a Service (VAaaS)

Tests systems and applications for vulnerabilities to address weaknesses.

Cross-Site Scripting (XSS) is a type of vulnerability that allows an attacker to inject malicious code into a website or web application. This code is executed by the victim’s web browser, allowing the attacker to steal sensitive information such as login credentials, or to perform actions on behalf of the victim. There are three types of XSS:

• Stored XSS: This type of XSS occurs when the malicious code is stored on the target server, such as in a database. When a victim retrieves the stored data, the malicious code is executed by their browser.

• Reflected XSS: This type of XSS occurs when the malicious code is included in a URL and is reflected back to the victim’s browser. The victim’s browser executes the code, allowing the attacker to perform actions on behalf of the victim.

• DOM-based XSS: This type of XSS occurs when the malicious code is injected into the Document Object Model (DOM) of the victim’s browser, rather than being delivered through the server. This can happen when the website or web application does not properly sanitize user input.

 

Examples:

An attacker injects a malicious script into a website’s search bar, which is then stored in the website’s database. When a victim searches for a term, the malicious script is executed by their browser, allowing the attacker to steal their login credentials.

An attacker includes a malicious script in a URL and lures a victim into clicking on it. The script is reflected back to the victim’s browser and executed, allowing the attacker to perform actions on behalf of the victim.

A web application does not properly sanitize user input, allowing an attacker to inject malicious code into the DOM of the victim’s browser. This can allow the attacker to steal sensitive information or perform actions on behalf of the victim.

 

In some cases, XSS vulnerabilities can be used to escalate privileges, allowing the attacker to gain access to restricted areas of the website or web application. This can be done by using the victim’s account to perform actions that would normally require higher privileges, or by using the XSS vulnerability to install malware on the victim’s device that grants the attacker higher privileges.

 

Here are some examples of vulnerable code in different programming languages:

 

JavaScript

 

function displayMessage(message) {
document.getElementById(“message”).innerHTML = message;
}

If an attacker can pass a malicious value for the message parameter, they can potentially execute arbitrary JavaScript code on the page. For example, if an attacker passes the following string as the message:

 

“; alert(“XSS!”); //

The resulting code would be:

 

function displayMessage(message) {
document.getElementById(“message”).innerHTML = “”; alert(“XSS!”); //”;

 

Which would execute an alert box with the message “XSS!” when the function is called.

 

PHP

 

$username = $_POST[‘username’];
echo “Welcome, $username;

 

If an attacker submits the following value for the username parameter:

 

‘; <script>alert(“XSS!”);</script>

 

The resulting code would be:

 

$username = ; <script>alert(“XSS!”);</script>‘;
echo “Welcome, $username”;

 

Which would execute an alert box with the message “XSS!” when the page is loaded.

 

Java

 

String username = request.getParameter(“username”);
out.println(“Welcome, “ + username);

 

If an attacker submits the following value for the username parameter:

 

“><script>alert(“XSS!);</script>

 

The resulting code would be:

 

String username = request.getParameter(“username”);
out.println(“Welcome, “ + “><script>alert(“XSS!“);</script>“);

 

Which would execute an alert box with the message “XSS!” when the page is loaded.

 

It’s important to note that these are just a few examples, and there are many other ways that XSS vulnerabilities can arise. To protect against XSS attacks, it’s important to properly sanitize input, escape output, and use appropriate HTTP headers to mitigate the risk of XSS attacks.

 

Methodology of Testing:

 

  1. Identify all input fields in the website or web application, including forms, search bars, and URL parameters.
  2. Attempt to inject malicious code into each input field. This can include HTML tags, JavaScript, and other types of code.
  3. If the injected code is reflected back to the browser and executed, the website or web application is vulnerable to XSS.
  4. Repeat the testing process for all input fields to ensure that all potential vulnerabilities have been identified.

Tools that can be used to test for and exploit XSS vulnerabilities:

 

Burp Suite: A toolkit for web application security testing that can be used to test for XSS vulnerabilities.

XSSer: An open-source tool for testing and exploiting XSS vulnerabilities.

XSStrike: A Python-based tool for detecting and exploiting XSS vulnerabilities.

BeEF: A tool that allows an attacker to control the victim’s browser through an XSS vulnerability.

 

Some popular exploits for XSS vulnerabilities:

 

Social engineering attacks: These involve tricking the victim into clicking on a malicious link or entering sensitive information into a form that has been injected with malicious code.

Malware installation: An XSS vulnerability can be used to install malware on the victim’s device, allowing the attacker to gain access to sensitive information or perform actions on behalf of the victim.

Credential theft: An XSS vulnerability can be used to steal the victim’s login credentials, allowing the attacker to gain access to restricted areas of a website or web application.

 

Top XSS last news:

 

CSS injection flaw patched in Acronis cloud management console

Open source CMS TYPO3 tackles XSS vulnerability 

XSS in Gmail’s AMP For Email earns researcher $5,000 

 

Websites that allow you to test for XSS vulnerabilities, including:

 

Hack.me: A websites that provides a variety of challenges for testing web application security skills, including XSS vulnerabilities.

XSS Challenge: A websites that provides a series of challenges for testing and improving your skills in finding and exploiting XSS vulnerabilities.

XSS Practice: A websites that provides a variety of challenges for testing and improving your skills in finding and exploiting XSS vulnerabilities.

 

Useful Courses for learning more about XSS vulnerabilities and how to test for and exploit them:

 

Web Application Hackers Handbook” by Dafydd Stuttard and Marcus Pinto: This book is a comprehensive guide to finding and exploiting web application vulnerabilities, including XSS vulnerabilities.

Cross-Site Scripting Attacks: XSS Exploits and Defense” by Seth Fogie and Mark Stanislav: This book provides a detailed overview of XSS vulnerabilities and how to defend against them.

Cross-Site Scripting Attacks: Classification, Attack, and Countermeasures by Brij B. Gupta and Pooja Chaudhary: This course, available on edX, covers the principles and techniques of web application security testing, including testing for XSS vulnerabilities.

 

Some of the top Common Vulnerabilities and Exposures (CVEs) related to XSS vulnerabilities:

 

CVE-2019-5108: A stored XSS vulnerability in the WordPress content management system that allowed an attacker to inject malicious code into the website’s database.

CVE-2018-7602: A reflected XSS vulnerability in the Drupal content management system that allowed an attacker to inject malicious code into a website through a URL.

CVE-2018-17082: A stored XSS vulnerability in the Magento e-commerce platform that allowed an attacker to inject malicious code into the website’s database.

 

List of Popular Exploits:

 

Social engineering attacks: These involve tricking the victim into clicking on a malicious link or entering sensitive information into a form that has been injected with malicious code.

Malware installation: An XSS vulnerability can be used to install malware on the victim’s device, allowing the attacker to gain access to sensitive information or perform actions on behalf of the victim.

Credential theft: An XSS vulnerability can be used to steal the victim’s login credentials, allowing the attacker to gain access to restricted areas of a website or web application.

 

List of Books with Review of Certain Vulnerability: Some books that provide a review of XSS vulnerabilities and how to defend against them include:

 

“Web Application Security: A Beginner’s Guide” by Bryan Sullivan: This book provides a beginner’s guide to web application security, including a review of XSS vulnerabilities and how to defend against them.
Hacking: The Art of Exploitation” by Jon Erickson: This book provides an in-depth review of various hacking techniques, including XSS vulnerabilities and how to exploit them.
Black Hat Python: Python Programming for Hackers and Pentesters” by Justin Seitz: This book provides a review of Python programming for hacking and penetration testing, including a chapter on exploiting XSS vulnerabilities.

List of Payloads Suitable for Vulnerability: Some payloads that can be used to exploit XSS vulnerabilities include:

 

JavaScript code: This can be used to perform actions on behalf of the victim, such as stealing login credentials or installing malware.

HTML tags: These can be used to modify the appearance of the website or web application, or to execute malicious code.

URL parameters: These can be used to inject malicious code into a website or web application through a URL.

 

Sigma Rules / Firewall Rules to Block or Stop Vulnerability: To block or stop XSS vulnerabilities, the following Sigma rules or firewall rules can be implemented:

 

Input validation: This involves verifying that all user input meets certain criteria, such as minimum length or allowed characters. This can help to prevent malicious code from being injected into the website or web application.

Sanitization: This involves removing or encoding potentially malicious code from user input. This can help to prevent the code from being executed by the victim’s browser.

Content Security Policy (CSP): This is a security feature that allows a website or web application to specify which sources are allowed to execute code in the victim’s browser. By specifying a strict CSP, it can be more difficult for an attacker to exploit an XSS vulnerability.

 

Useful Services: Some useful services for addressing XSS vulnerabilities include:

 

Web application firewall (WAF): A WAF is a security system that monitors and controls incoming and outgoing traffic to a website or web application. It can be configured to block or mitigate XSS vulnerabilities.

Security testing services: There are several companies that offer services to test websites and web applications for vulnerabilities, including XSS vulnerabilities. These services can help to identify and fix vulnerabilities before they are exploited.

 

Some steps that can be taken to mitigate the risk of XSS vulnerabilities include:

 

Implementing input validation and sanitization: This can help to prevent malicious code from being injected into the website or web application.

Using a content security policy: This can help to specify which sources are allowed to execute code in the victim’s browser, making it more difficult for an attacker to exploit an XSS vulnerability.

Regularly patching and updating the website or web application: This can help to fix known vulnerabilities and prevent them from being exploited.

Educating users: Training users to recognize and avoid suspicious links and forms can help to prevent them from falling victim to XSS attacks.

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