Session Management

Web applications are built on the stateless HTTP protocol, so session management is an application-level responsibility. Session security is critical to the overall security of an application.

The following practices improve the security of your Web application's session management:

• Use SSL to protect session authentication cookies .

• Encrypt the contents of the authentication cookies .

• Limit session lifetime .

• Protect session state from unauthorized access .

Use SSL to Protect Session Authentication Cookies

Do not pass authentication cookies over HTTP connections. Set the secure cookie property within authentication cookies, which instructs browsers to send cookies back to the server only over HTTPS connections. For more information, see Chapter 10, "Building Secure ASP.NET Web Pages and Controls."

Encrypt the Contents of the Authentication Cookies

Encrypt the cookie contents even if you are using SSL. This prevents an attacker viewing or modifying the cookie if he manages to steal it through an XSS attack. In this event, the attacker could still use the cookie to access your application, but only while the cookie remains valid.

Limit Session Lifetime

Reduce the lifetime of sessions to mitigate the risk of session hijacking and replay attacks. The shorter the session, the less time an attacker has to capture a session cookie and use it to access your application.

Protect Session State from Unauthorized Access

Consider how session state is to be stored. For optimum performance, you can store session state in the Web application's process address space. However, this approach has limited scalability and implications in Web farm scenarios, where requests from the same user cannot be guaranteed to be handled by the same server. In this scenario, an out-of-process state store on a dedicated state server or a persistent state store in a shared database is required. ASP.NET supports all three options.

You should secure the network link from the Web application to state store using IPSec or SSL to mitigate the risk of eavesdropping. Also consider how the Web application is to be authenticated by the state store. Use Windows authentication where possible to avoid passing plaintext authentication credentials across the network and to benefit from secure Windows account policies.