Cross-Site Scripting (XSS)
Cross-Site Scripting (XSS) is a type of security vulnerability commonly found in web applications. It occurs when an attacker injects malicious scripts into web pages viewed by other users. These scripts can be written in various languages such as JavaScript, HTML, or VBScript. When unsuspecting users visit the compromised page, their browsers execute the malicious script, allowing the attacker to steal sensitive information, hijack user sessions, or deface websites.
XSS attacks can be classified into three main types:
Reflected XSS: In this type of attack, the malicious script is reflected off a web server. Typically, the attacker tricks a user into clicking a specially crafted link that contains the malicious payload. The server then includes this payload in the response sent back to the user's browser, which executes the script within the context of the vulnerable page.
Stored XSS: Also known as persistent XSS, this attack involves injecting malicious scripts directly into a website's database or storage. When other users visit the affected page, the script is served along with the legitimate content, executing in their browsers and potentially causing harm.
DOM-based XSS: This type of XSS occurs when the client-side JavaScript code manipulates the DOM (Document Object Model) in an unsafe manner. The attacker can inject malicious code into the DOM environment, exploiting vulnerabilities in the client-side scripts themselves rather than the server-side code.
Preventing XSS attacks requires a combination of secure coding practices and input validation techniques. Developers should:
- Properly encode and sanitize user input to prevent it from being interpreted as executable code.
- Implement content security policies (CSP) to restrict the sources from which content can be loaded.
- Use frameworks and libraries that provide built-in protection against XSS vulnerabilities.
- Regularly update software to patch known security flaws.
- Educate users about the risks of clicking on suspicious links and encourage them to use modern, up-to-date browsers with built-in security features.