Cross-Site Scripting (XSS)
A web security vulnerability where attackers inject malicious scripts into web applications.
Understanding Cross-Site Scripting (XSS)
XSS exploits weaknesses in how web applications handle user input and output. When a web page does not properly sanitize user-supplied data before displaying it, an attacker can inject harmful JavaScript that runs in the browser of another user. This allows attackers to steal cookies, modify website content, or perform actions on behalf of a logged-in user without their consent.
Types of Cross-Site Scripting
Stored XSS (Persistent XSS)
The malicious script is permanently stored on the server (e.g., in a database or comment section).
Affects multiple users whenever they load the compromised page.
Example: An attacker injects a malicious JavaScript payload in a user profile field, which executes when others visit the profile.
Reflected XSS (Non-Persistent XSS)
The malicious script is included in a URL or form input and executed when the victim interacts with it.
Requires social engineering (e.g., sending phishing links).
Example: A crafted URL containing JavaScript executes in a victim’s browser when clicked.
DOM-Based XSS
The script is executed within the victim's browser due to insecure handling of user input in JavaScript.
Does not require server-side interaction.
Example: A web application dynamically modifies the webpage using user input without proper validation.
Challenges and Considerations
Difficult Detection: XSS payloads can be obfuscated and bypass filters.
Legacy Systems: Older web applications may lack security patches.
Third-Party Components: Vulnerable JavaScript libraries can introduce XSS risks.
User Awareness: Social engineering plays a role in successful attacks.