Defend Against XSS Attacks with Open Source Vulnerability Scanners

Cross site-scripting (XSS), an attack in which a threat actor injects malicious executable scripts into the code of a trusted application or website, is a prevalent and serious threat to developers and their projects. It is estimated that more than 60% of web applications are susceptible to XSS attacks, which eventually account for more than 30% of all web application attacks.

If the proper security measures have not been taken to secure applications and websites against these attacks, XSS can enable an attacker to steal the user’s active session cookie. The higher the compromised user's privileges are in an application, the more critical the impact of the attack is likely to be, and if users input sensitive, personally identifiable information, the repercussions of an attack can be severe. 

Luckily, there are many great open source cross-site scripting vulnerability scanners available to Linux users that enable developers to find and fix XSS vulnerabilities before they are exploited by attackers. This article will introduce six great open source cross-site scripting vulnerability scanners you should know about that will help you protect your websites and applications against attacks leading to compromise

What Is XSS & How Does It Work?

As previously mentioned, cross site scripting (XSS) is an attack in which an attacker injects malicious executable scripts into the code of a trusted application or website. Attackers often initiate an XSS attack by tricking a user into clicking through a malicious link. If the app or website lacks proper data sanitization, the malicious link executes the attacker’s chosen code on the user’s system. The following criteria must be met in order for an XSS attack to occur:

1. Data enters a Web application through an untrusted source, most frequently a web request.
2. The data is included in dynamic content that is sent to a web user without being validated for malicious content.

The variety of attacks that can be carried out based on XSS is almost limitless, but these attacks commonly include transmitting private data to the attacker, redirecting the victim to web content controlled by the attacker, or performing other malicious operations on the user’s machine under the guise of the vulnerable site.

Types of XSS Vulnerabilities 

There are multiple types or categories of cross-site scripting (XSS) vulnerabilities you should be aware of: 

• Reflected XSS (Non-Persistent or Type I) occurs when user input is immediately returned by a web application in an error message, search result, or any other response that includes some or all of the input provided by the user as part of the request, without that data being made safe to render in the browser, and without permanently storing the user provided data.
• Stored XSS (Persistent or Type II) Stored XSS generally occurs when user input is stored on the target server, such as in a database, in a message forum, visitor log, comment field, etc. Then, a victim is able to retrieve the stored data from the web application without that data being made safe to render in the browser. 
• DOM Based XSS (Type-0) is a form of XSS where the entire tainted data flow from source to sink takes place in the browser, i.e., the source of the data is in the DOM, the sink is also in the DOM, and the data flow never leaves the browser. 
• Server XSS occurs when untrusted user supplied data is included in an HTTP response generated by the server. 
• Client XSS occurs when untrusted user supplied data is used to update the DOM with an unsafe JavaScript call.

Tips to Protect Against XSS Attacks 

Best practices to prevent XSS attacks include the following:

• Never trust user input.
• Implement output encoding.
• Perform user input validation.
• Use a web application firewall (WAF).
• Use one of the open source XSS vulnerability scanners discussed in this article.
• Implement a defense in depth strategy for securing websites and applications.
• Ensure that web application development aligns with OWASP’s XSS Prevention Cheat Sheet.
• After remediation, perform penetration testing to confirm it was successful.

Top Open Source Cross-Site Scripting Vulnerability Scanners

Open-source cross-site scripting (XSS) vulnerability scanners are tools designed to help identify and prevent XSS attacks by automating the process of searching for potential vulnerabilities in web applications. Here are some of the top open-source XSS scanners.

Damn Small XSS Scanner 

Damn Small XSS Scanner (DSXS) is a free and open-source cross-site scripting (XSS) vulnerability scanner. XSS is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. DSXS is designed to help identify and prevent XSS attacks by automating the process of searching for potential vulnerabilities in web applications.

Some of the key features of DSXS include:

• Simplicity: DSXS is designed to be a simple and easy-to-use tool for identifying XSS vulnerabilities, making it accessible to a wide range of users, including those with limited technical expertise.
• Automated scanning: DSXS automates the process of searching for XSS vulnerabilities in web applications, reducing the time and effort required to identify potential security risks.
• Payload generation: DSXS provides a range of payloads to test for XSS vulnerabilities, allowing administrators to test for a wide range of potential security risks.
• Reporting: DSXS provides basic reporting of the results of its scans, including information on the type of vulnerability found, the payload used, and the affected URL.

What makes DSXS unique is its simplicity. Its straightforward and easy-to-use interface makes it a good choice for users who may be new to XSS scanning and web application security. Additionally, its range of payloads provides a comprehensive approach to testing for XSS vulnerabilities in web applications.

This tool is a great tool to use for learning purposes because of its small understandable code base. Below you will how Damn Small XSS is utilized in a actual scan/attack:

Pwnxss 

Pwnxss is a free and open-source cross-site scripting (XSS) vulnerability scanner. XSS is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. PwnXSS is designed to help identify and prevent XSS attacks by automating the process of searching for potential vulnerabilities in web applications.

Some of the key features of PwnXSS include:

• Automated scanning: PwnXSS automates the process of searching for XSS vulnerabilities in web applications, reducing the time and effort required to identify potential security risks.
• Real-time detection: PwnXSS provides real-time detection of XSS vulnerabilities, allowing administrators to take immediate action to prevent attacks.
• Payload generation: PwnXSS provides a range of payloads to test for XSS vulnerabilities, allowing administrators to test for a wide range of potential security risks.
• Reporting: PwnXSS provides detailed reporting of the results of its scans, including information on the type of vulnerability found, the payload used, and the affected URL.

What makes PwnXSS unique is its real-time detection of XSS vulnerabilities and its ability to provide instant feedback on potential security risks allows administrators to take immediate action to prevent attacks. Additionally, its range of payloads provides a comprehensive approach to testing for XSS vulnerabilities in web applications.

If you want to begin using Pwnxss here are the steps:

• pip install bs4
• pip install requests
• git clone https://github.com/pwn0sec/PwnXSS
• chmod 755 -R PwnXSS
• cd PwnXSS
• python3 pwnxss.py --help
• python3 pwnxss.py -u https://testphp.vulnweb.com

W3af 

W3af is a free and open-source web application security scanner that is designed to identify and exploit various types of vulnerabilities, including cross-site scripting (XSS) vulnerabilities. XSS is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. w3af automates the process of searching for potential vulnerabilities in web applications and provides a comprehensive solution for identifying and preventing XSS attacks.

Some of the key features of w3af include:

• Automated scanning: w3af automates the process of searching for XSS vulnerabilities in web applications, reducing the time and effort required to identify potential security risks.
• Multiple vulnerability detection: w3af is designed to detect a wide range of vulnerabilities, including XSS, SQL injection, and others, making it a comprehensive security tool for web applications.
• Customizable scan profiles: w3af provides a range of customizable scan profiles, allowing administrators to tailor the scanning process to their specific needs.
• Reporting: w3af provides detailed reporting of the results of its scans, including information on the type of vulnerability found, the payload used, and the affected URL.

What makes w3af unique is its comprehensive approach to web application security. Its ability to detect a wide range of vulnerabilities and its customizable scan profiles make it a flexible and effective tool for identifying and preventing XSS attacks and other types of security threats.

Below you will see how W3af is used:

Audit - plugins that are used to detect vulnerabilities in the URL’s or forms provided by discovery plugins.

Brute Force - plugins that can be used to brute force login forms as well as http-auth logins.

XssPy 

XssPy is a free and open-source cross-site scripting (XSS) vulnerability scanner. XSS is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. XssPy is designed to help identify and prevent XSS attacks by automating the process of searching for potential vulnerabilities in web applications.

Some of the key features of XssPy include:

• Automated scanning: XssPy automates the process of searching for XSS vulnerabilities in web applications, reducing the time and effort required to identify potential security risks.
• Multiple injection methods: XssPy supports multiple injection methods, including GET and POST requests, allowing for a more comprehensive scan of web applications.
• Custom payloads: XssPy allows administrators to use custom payloads when searching for XSS vulnerabilities, providing more flexibility and control over the scanning process.
• Reporting: XssPy provides detailed reporting of the results of its scans, including information on the type of vulnerability found, the payload used, and the affected URL.

What makes XssPy unique is its focus on automating the process of searching for XSS vulnerabilities, allowing administrators to quickly identify and address potential security risks. It also supports multiple injection methods and custom payloads, providing more comprehensive and flexible scanning capabilities compared to other XSS vulnerability scanners.

Vega  

Vega  is a free and open-source web application security scanner specifically designed to identify cross-site scripting (XSS) vulnerabilities. XSS is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. Vega is designed to help identify and prevent XSS attacks by automating the process of searching for potential vulnerabilities in web applications.

Some of the key features of Vega include:

• Graphical user interface: Vega provides a graphical user interface that makes it easy to use, even for non-technical users.
• Automated scanning: Vega automates the process of searching for XSS vulnerabilities in web applications, reducing the time and effort required to identify potential security risks.
• Vulnerability detection: Vega uses a combination of techniques, including dynamic analysis and signature matching, to detect XSS vulnerabilities in web applications.
• Reporting: Vega provides detailed reporting of the results of its scans, including information on the type of vulnerability found, the payload used, and the affected URL.

What makes Vega unique is its user-friendly graphical interface, which makes it accessible to a wider range of users, including non-technical users. Additionally, Vega's combination of dynamic analysis and signature matching provides a comprehensive and effective approach to identifying XSS vulnerabilities in web applications. 

OWASP Xenotix XSS

OWASP Xenotix is a free and open-source cross-site scripting (XSS) vulnerability scanner. XSS is a type of security vulnerability that allows an attacker to inject malicious code into a web page viewed by other users. OWASP Xenotix is designed to help identify and prevent XSS attacks by automating the process of searching for potential vulnerabilities in web applications.

Some of the key features of OWASP Xenotix include:

• Automated scanning: OWASP Xenotix automates the process of searching for XSS vulnerabilities in web applications, reducing the time and effort required to identify potential security risks.
• Multiple injection methods: OWASP Xenotix supports multiple injection methods, including GET and POST requests, allowing for a more comprehensive scan of web applications.
• Custom payloads: OWASP Xenotix allows administrators to use custom payloads when searching for XSS vulnerabilities, providing more flexibility and control over the scanning process.
• Reporting: OWASP Xenotix provides detailed reporting of the results of its scans, including information on the type of vulnerability found, the payload used, and the affected URL.

What makes OWASP Xenotix unique is its focus on automation and flexibility. Its support for multiple injection methods and the ability to use custom payloads provides a comprehensive and flexible approach to identifying XSS vulnerabilities in web applications. Additionally, being part of the OWASP (Open Web Application Security Project) community provides a level of credibility and reliability for the tool.

Our Thoughts

Cross site-scripting (XSS) is a common and severe threat to website and application developers and their projects. A successful attack can lead to the compromise of sensitive personal or financial information, making it imperative that measures are taken to protect against XSS attacks.

By implementing the best practices and using the open source XSS vulnerability scanners discussed in this article, you can secure your work and your sensitive data against attacks and compromise.