Description: Cross-Site Scripting (XSS) is a security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This technique relies on the execution of JavaScript code in the victim’s browser, which can lead to the theft of sensitive information such as session cookies, user credentials, or personal data. XSS is classified into several categories, including reflected, stored, and DOM-based XSS, each with different exploitation methods and consequences. The nature of XSS lies in the trust that browsers place in the content presented, allowing a malicious script to execute as if it were part of the legitimate page. Preventing XSS involves implementing security measures such as input validation and sanitization, using content security policies (CSP), and properly encoding data before it is sent to the browser. Given its prevalence and potential impact on web application security, XSS is a critical topic in the field of cybersecurity and secure software development.
History: The XSS vulnerability was first identified in 1999 by security researcher Jeremiah Grossman. Since then, it has evolved over time, becoming one of the most common vulnerabilities in web applications. As web technologies have advanced, so have the techniques for exploiting XSS, leading to a more rigorous focus on application security and the implementation of best practices to mitigate these risks.
Uses: XSS is primarily used to steal sensitive information from users, such as login credentials and personal data. It can also be used to carry out phishing attacks, redirect users to malicious sites, or propagate malware. Web applications that do not implement adequate security measures are particularly vulnerable to these attacks.
Examples: An example of reflected XSS is when an attacker sends a malicious link to a user, and upon clicking it, a script executes that steals their session cookie. In the case of stored XSS, an attacker can inject a script into a forum or comment system, which then executes every time a user visits that page. An example of DOM-based XSS is when a script manipulates the Document Object Model (DOM) of a web page to execute malicious code in the user’s browser.
