XSS

Definition

Cross-site scripting attacks injecting malicious code into websites.

Technical Details

Cross-site scripting (XSS) is a type of security vulnerability typically found in web applications that allows an attacker to inject malicious scripts into content from otherwise trusted websites. XSS attacks enable attackers to execute scripts in a victim's web browser, which can lead to unauthorized actions, data theft, session hijacking, or redirection to malicious websites. There are three main types of XSS attacks: Stored XSS, where the malicious script is stored on the server and served to users; Reflected XSS, where the script is reflected off a web server; and DOM-based XSS, where the vulnerability exists in the client-side code rather than the server-side code. Mitigation strategies include input validation, output encoding, and the use of Content Security Policy (CSP).

Practical Usage

XSS vulnerabilities are exploited in various real-world scenarios, often targeting high-traffic websites where user interaction is frequent. For instance, an attacker may inject a script into a comment section of a blog, which could steal cookies and session tokens from users who view that comment. In business applications, XSS can be used to inject malicious scripts into forms, leading to data exfiltration or unauthorized transactions. Developers implement security measures such as sanitizing user input and employing frameworks that automatically encode output to reduce the risk of XSS.

Examples

• An attacker posts a comment containing a malicious script on a public forum, which when viewed by other users, executes and steals their session cookies.
• A phishing attack where an email contains a link that redirects to a compromised site, which uses XSS to steal credentials from users who log in.
• A web application that allows users to submit HTML content without proper sanitization, leading to an attack where a user’s browser executes an injected script that captures keystrokes.

Related Terms