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At a basic level, understanding session management is straightforward. When a user authenticates to a server, it creates and sends a token to the browser so that the browser can share the authentication information, making future access easier. However, managing session expiration and ensuring that the session token is valid for the requestor becomes challenging. Further, as users increasingly adopt the application, horizontal scaling impacts the load balancer’s ability to appropriately route traffic and maintain service speed. 

For developers, understanding secure session management’s impact on security and steps to mitigate risks arising from improper session management is critical to the application’s security. 

​​Understanding session management security

Session management refers to the process of destroying session tokens for the following events:

  • User manual log out: user interface controls that allow people to log out
  • Direct session termination: administrator-forced logout 
  • Session timeout: automatic logout after a period of inactivity

A simple session management flow looks like this:

  • User authenticates to the application using credentials
  • Server receives the request, creating a session
  • Server responds to request by sending the application an access token
  • Application uses the access token for subsequent requests to the server
  • Server checks and validates the access token when it receives the request so the user can perform authorized actions
  • Process repeats until the user logs out or the session expires. 
  • Access tokens are deleted.

Since a session token uniquely identifies a user’s session, each request and response associated with one allows the application to connect a specific user with the client using it. Without correct session management, attackers can exploit an authenticated user session to undermine the applications security. 

Attacks Arising from Broken Authentication and Session Management Vulnerabilities

Identification and Authentication Failures, formerly Broken Authentication, is one of the OWASP Top 10 application vulnerability categories. Within this vulnerability category, attackers can exploit a session management vulnerability during the following attack types.

Session ID Hijacking

Attackers can steal or predict a valid session token by performing a standard request to observe a session token that is unencrypted, easily decrypted, or guessable. For example, some implementations include easily guessable information in their session ID, like:

  • Username
  • Timestamps
  • Client IP address

Attackers that understand the session ID’s structure can implement a brute force technique to generate and test various session ID values until they gain unauthorized access to the application. 

Cross-Site Scripting (XSS)

Applications may use cookies to store the session ID. By identifying a vulnerable input in the web application, they can inject a malicious cookie stealer script, pointing to a web-server hosted file that can be resolved outside the local network.  With access to the session token, they can hijack the session ID to compromise the application’s sensitive data. 

Session Fixation Attacks

A web application server is often a “stateful server,” meaning that it retains persistent information about the user’s session. In a session fixation attack, the threat actors use social