What is Cross-Site Scripting (XSS)?
Cross-Site Scripting (XSS) is a security vulnerability typically found in web applications that allows attackers to inject malicious scripts into content that is sent to users. This occurs when an application includes untrusted data on a webpage without proper validation or escaping, enabling attackers to run scripts in the context of a user's browser.
XSS attacks can be categorized into three main types: Stored XSS, where the malicious script is stored on the server (e.g., in a database) and later served to users; Reflected XSS, where the script is reflected off a web server immediately after being sent by the user; and DOM-based XSS, which occurs when the client-side scripts modify the DOM in an unsafe manner.
Successful XSS exploits can lead to a variety of malicious activities such as session hijacking, redirecting users to malicious sites, or spreading malware. By executing scripts in a user’s session, attackers can steal sensitive information, such as cookies or credentials, without the user’s knowledge.
To mitigate XSS vulnerabilities, developers can implement several security practices, including proper input validation, output encoding, and employing Content Security Policy (CSP) to restrict the origins of executable scripts. Developing a security-first mindset during the design and implementation phases is essential for protecting web applications from XSS threats.