Cookie Security
Cookie security refers to the set of attributes, configurations, and best practices used to protect HTTP cookies from theft, tampering, and misuse. Properly secured cookies are essential for maintaining session integrity and preventing attacks like session hijacking and CSRF.
HTTP cookies are the primary mechanism for maintaining state in web applications, storing session identifiers, authentication tokens, and user preferences. Because cookies are automatically sent with every request to the associated domain, they are a high-value target for attackers. Securing cookies is therefore critical to overall application security.
Several cookie attributes provide security protections. The Secure flag ensures the cookie is only transmitted over HTTPS connections, preventing interception over unencrypted channels. The HttpOnly flag prevents JavaScript from accessing the cookie, mitigating XSS-based session theft. The SameSite attribute controls whether cookies are sent with cross-origin requests, providing protection against CSRF attacks with values of Strict (never sent cross-origin), Lax (sent with top-level navigations), or None (always sent, requires Secure).
The Domain and Path attributes control the scope of cookie transmission. Setting the Domain attribute too broadly (such as .example.com) exposes the cookie to all subdomains, increasing the attack surface. The Path attribute can limit cookie transmission to specific URL paths, though it provides limited security benefit since JavaScript from other paths on the same origin can still access the cookie.
Additional best practices include setting appropriate expiration times, using cookie prefixes (__Secure- and __Host-) for additional browser-enforced restrictions, encrypting or signing cookie values to prevent tampering, minimising the amount of data stored in cookies, and regularly rotating session identifiers. Cookie security should be part of a comprehensive session management strategy.