XSS
XSS is the acronym for Cross-Site Scripting.
Cross-Site Scripting
A type of security vulnerability typically found in web applications. XSS enables attackers to inject client-side scripts into web pages viewed by other users. This is often used to bypass access controls such as the same-origin policy, which is meant to segregate different websites from each other in a user’s browser.
XSS attacks can occur whenever an application includes untrusted data in a new web page without properly validating or escaping it. An attacker can use XSS to send a malicious script to an unsuspecting user, and the end user’s browser wouldn’t know that the script shouldn’t be trusted. The script can then steal sensitive data like authentication credentials, session cookies, or other sensitive information stored by the browser.
There are three main types of XSS attacks:
- Stored XSS Attacks: The application stores user input and then displays it on other pages without validating or sanitizing the input. The malicious script is then permanently part of the pages it was stored on.
- Reflected XSS Attacks: The application includes user input as part of its immediate response to a user’s request, without validating or sanitizing the input.
- DOM-based XSS Attacks: The web application’s client-side scripts write user-provided data to the Document Object Model (DOM). The data is subsequently read from the DOM by the web application and output to the browser.
The term XSS was coined in the 1990s, but the concept of injecting malicious code into websites dates back even further. It’s important to clarify that XSS wasn’t implemented. Instead, it’s a type of vulnerability that occurs due to a lack of proper data handling by web applications. Therefore, the primary prevention methods for XSS include input validation, output encoding, and setting a robust Content Security Policy.
XSS continues to be a frequent and high-impact vulnerability type, especially in complex web applications. Various mitigation strategies and frameworks, including CSP, have been developed to tackle this persistent issue.
- Abbreviation: XSS
