10 PHP Session Variables Best Practices

PHP session variables are an important part of web development. They allow developers to store user data and access it across multiple pages. However, if not used correctly, session variables can be a security risk.

In this article, we will discuss 10 best practices for using PHP session variables. We will look at how to create secure session variables, how to store them safely, and how to delete them when they are no longer needed. Following these best practices will help ensure that your website is secure and your user data is protected.

1. Set the session cookie to HttpOnly

HttpOnly is an additional flag included in a Set-Cookie HTTP response header. When set, it instructs the browser to not expose the cookie through channels other than HTTP (e.g., JavaScript). This helps prevent malicious scripts from stealing session cookies and hijacking user sessions. To enable HttpOnly for PHP session variables, add the following line of code to your php.ini file:

session.cookie_httponly = 1

2. Set a secure flag on the session cookie

The secure flag is an optional attribute that can be set when a cookie is created. When the secure flag is set, the browser will only send the cookie over HTTPS connections. This prevents attackers from intercepting the session cookie and using it to hijack the user’s session.

To set the secure flag on the session cookie in PHP, use the session_set_cookie_params() function. The first parameter of this function is an array containing various options for the cookie, including the secure flag. To set the secure flag, pass an array with the ‘secure’ key set to true. For example:
session_set_cookie_params(array(‘secure’ => true));

3. Use random and long session IDs

Random session IDs are important because they make it difficult for attackers to guess a valid session ID. If an attacker can guess the session ID, they can hijack the user’s session and gain access to their account or other sensitive information. To prevent this from happening, random session IDs should be generated using a cryptographically secure pseudorandom number generator (CSPRNG).

Long session IDs also help protect against brute-force attacks, as there is a much larger search space for an attacker to try and guess a valid session ID. The longer the session ID, the more secure it will be. A good rule of thumb is to use at least 32 characters in length.

To generate random and long session IDs in PHP, you can use the function openssl_random_pseudo_bytes(). This function takes two parameters: the length of the string to generate and whether or not it should be cryptographically strong. It is recommended that you set the second parameter to true so that a CSPRNG is used.

4. Regenerate session IDs regularly

When a user logs in, the server creates a unique session ID and stores it on both the server and the client’s computer. This allows the server to identify the user when they make subsequent requests. However, if an attacker is able to obtain the session ID, they can impersonate the user and gain access to their account. To prevent this from happening, regenerating session IDs regularly helps ensure that any stolen session IDs become invalid quickly.

To regenerate session IDs regularly, PHP provides the session_regenerate_id() function. This function generates a new session ID and replaces the old one with it. It also deletes the old session data associated with the old session ID. The frequency of regeneration should be based on the sensitivity of the application and the amount of time a user spends logged in. For example, for applications with high security requirements, session IDs could be regenerated every few minutes.

5. Store sessions in a database

Storing sessions in a database provides an extra layer of security. By storing session data in the database, it is not accessible to anyone who might gain access to the server file system. This helps protect sensitive information stored in the session from being accessed by malicious actors.

It also allows for more flexibility when managing user sessions. For example, if you need to track user activity across multiple servers, you can easily do so with a centralized database. Additionally, if you need to expire or delete certain sessions, this can be done quickly and easily using SQL queries.

Furthermore, databases are designed to handle large amounts of data efficiently, making them ideal for storing session variables. Databases provide better performance than flat files, which can become slow as they grow larger.

6. Avoid storing sensitive data in sessions

Storing sensitive data in sessions can be a security risk, as it is stored on the server and could potentially be accessed by malicious actors. To avoid this, developers should use encryption to store any sensitive information that needs to be stored in session variables. This will ensure that even if someone were to gain access to the session variable, they would not be able to read or understand the data. Additionally, developers should also consider using an alternative storage method for sensitive data such as a database or file system. This way, the data is kept separate from the session variables and is more secure.

7. Don’t use $_SESSION for authentication

Using $_SESSION for authentication can be a security risk because it is stored in plain text on the server. This means that if an attacker were to gain access to the server, they would have access to all of the user’s session data. Additionally, since the session data is stored on the server, there is no way to verify that the user has not tampered with the data.

A better approach is to use a secure token-based authentication system. With this method, each request from the client includes a unique token which is then verified by the server. The token is generated using a cryptographic algorithm and is cryptographically signed so that any tampering will be detected. This ensures that only authorized requests are processed and that the user’s session data remains secure.

8. Destroy sessions when users log out

When a user logs out, it is important to destroy the session variables associated with that user. This ensures that any sensitive information stored in those variables cannot be accessed by anyone else who may gain access to the same computer or device. It also prevents malicious users from hijacking the session and using it for their own purposes.

To destroy a session, PHP provides the session_destroy() function. This function will unset all of the session variables and clear the session cookie on the client side. Additionally, it will delete the session file from the server. Once this is done, the session is completely destroyed and no one can use it again.

9. Set an appropriate session timeout value

The session timeout value is the amount of time a user can remain inactive before their session expires. This helps to ensure that sessions are not left open indefinitely, which could lead to security issues such as unauthorized access or data leakage. Setting an appropriate session timeout value also ensures that resources are not wasted on idle sessions.

To set the session timeout value in PHP, use the session_set_cookie_params() function. This function takes three parameters: lifetime (the number of seconds until the cookie expires), path (the directory where the cookie will be available), and domain (the domain for which the cookie is valid). The lifetime parameter should be set to the desired session timeout value. For example, if you want the session to expire after 30 minutes of inactivity, you would set the lifetime parameter to 1800 (30 minutes x 60 seconds = 1800 seconds).

10. Enable strict mode for session variables

Strict mode helps to prevent session hijacking by making sure that the browser used to create a session is the same one used to access it. This is done by checking the user agent and IP address of the client against the values stored in the session data. If either value does not match, then the session will be invalidated and the user will have to log in again.

Enabling strict mode for session variables can be done by setting the ‘session.use_strict_mode’ directive in the php.ini file. Once enabled, all new sessions created will use this security measure. It is also possible to enable strict mode on an existing session by calling the session_set_cookie_params() function with the ‘httponly’ parameter set to true.