HTTP Cookies: Complete Security Guide

HTTP Cookies Diagram

HTTP cookies are small blocks of data created by a web server while a user is browsing a website and placed on the user's computer or other device by the user's web browser. Cookies are placed on the device used to access a website, and more than one cookie may be placed on a user's device during a session.

What are HTTP Cookies?

Cookies are used to remember stateful information for the stateless HTTP protocol. They can be used for various purposes, including:

  • Session management: Logins, shopping carts, game scores, or anything else the server should remember
  • Personalization: User preferences, themes, and other settings
  • Tracking: Recording and analyzing user behavior

Cookie Attributes

Cookies have several attributes that control their behavior and security:

  • Name=Value: The actual data stored in the cookie.
  • Domain: Specifies the domain for which the cookie is valid.
  • Path: Specifies the URL path for which the cookie is valid.
  • Expires or Max-Age: Defines the lifetime of the cookie.
  • Secure: Indicates that the cookie should only be transmitted over HTTPS.
  • HttpOnly: Prevents client-side scripts from accessing the cookie.
  • SameSite: Controls whether the cookie is sent with cross-site requests.

Security Considerations

Cookies can be vulnerable to several security threats:

  • Cross-Site Scripting (XSS): Attackers can inject malicious scripts to steal cookies.
  • Cross-Site Request Forgery (CSRF): Attackers can trick users into performing actions they didn't intend to.
  • Cookie Hijacking: Attackers can intercept and steal cookies.

Best Practices

To mitigate these risks, follow these best practices:

  • Use the Secure attribute to ensure cookies are only transmitted over HTTPS.
  • Use the HttpOnly attribute to prevent client-side scripts from accessing cookies.
  • Set the SameSite attribute to Strict or Lax to protect against CSRF attacks.
  • Regularly review and update your cookie policies.

Learn More

For more information on HTTP cookies, refer to the following resources: