XSS (Cross-Site Scripting) What Is It and How to Prevent It?
XSS (Cross-Site Scripting) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users.
Raul Cano on July 15, 2024What is XSS (Cross-Site Scripting)?
XSS (Cross-Site Scripting) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. These scripts can be used to steal sensitive information, such as cookies, session tokens, or other personal data. XSS attacks can be classified into three main types:
- Stored XSS: The attacker injects a malicious script into a web page, which is then stored on the server and executed whenever a user visits the page.
- How do they inject the script? They can do it through a comment form, a search bar, or any other input field that allows user input.
- Reflected XSS: The attacker injects a malicious script into a URL, which is then reflected back to the user and executed by the browser.
- DOM-based XSS: The attacker injects a malicious script into the DOM (Document Object Model) of a web page, which is then executed by the browser.
How Does XSS Work?
XSS attacks work by exploiting vulnerabilities in web applications that allow user input to be executed as code. This can happen when the application fails to properly validate and sanitize user input, allowing attackers to inject malicious scripts into web pages. Once the script is executed by the browser, it can access sensitive information, such as cookies, session tokens, or other personal data.
How to Prevent XSS Attacks?
To prevent XSS attacks, web developers should follow best practices for secure coding and implement the following measures:
- Input Validation: Validate and sanitize all user input to prevent malicious scripts from being executed.
- Output Encoding: Encode all user input before displaying it on a web page to prevent script injection.
- Content Security Policy (CSP): Implement a Content Security Policy to restrict the sources from which scripts can be loaded on a web page.
- HTTPOnly Cookies: Use the HTTPOnly flag to prevent cookies from being accessed by client-side scripts.
- X-XSS-Protection Header: Enable the X-XSS-Protection header to prevent browsers from executing malicious scripts.
It will really depend on the technology stack you are using, but these are some general guidelines.