Are Browser Sessions Immutable, or Can Users Alter Website Session IDs?

Session Hijacking in PHP: Understanding the Client-Server Distinction

While researching session hijacking in PHP, one may encounter the question of whether users can alter their website session. Can they modify their initial session (labeled as X) to Y or Z?

Traditionally, sessions are believed to be immutable, established by the browser. However, the documentation surrounding session hijacking suggests otherwise, prompting a reassessment of this assumption.

Delving into the Client-Server Distinction

To understand session hijacking, it's crucial to recognize the distinction between client-side and server-side sessions.

Server-Side Session: Changeable Identifier but Protected Content

Server-side sessions, commonly referred to as sessions, consist of an ID (passed between client and server), content (maintained on the server), and potential additional attributes like last access time. Typically, the session ID is conveyed through a cookie named "PHPSESSID" by default in PHP. If cookies are unavailable, PHP may switch to a query string parameter with the same name.

This cookie or query parameter can be modified, allowing the session identifier to be manipulated as well. However, the content of the session (representing, for instance, a user's login status) remains untouched since it's stored on the server and can only be altered by a PHP script running on that specific server.

Protecting Against Session Hijacking

To mitigate session hijacking, other methods for identifying users in a given session are required. This can involve analyzing the user agent, IP address, or a separate cookie. While alternative session storage options like database storage or custom directory paths provide workarounds, implementing HTTPS for any session-involving interaction remains the most effective way to prevent session cookie theft.

Client-Side Session: A Collection of Views and Data

In contrast to server-side sessions, client-side sessions have a broader definition, encompassing various contexts. These may include session managers that restore open pages upon browser launch, session cookies, and sessionStorage.

Browser sessions can be conceptualized as a compilation of views (tabs, windows) and their related data. Each view possesses a history, current page, and associated page data. Shared domains enable sharing of page data for various pages within a single browser session, while separate domains or sessions prevent data interchange.

Closing the browser finishes all active sessions, and depending on the browser's settings, parts of the session (like histories and sessionStorage) could be stored for re-opening by a session manager. Session cookies are specific to their respective session and are discarded upon its conclusion.

Control of Browser Sessions

The notion of browser sessions is not static but influenced by the specific browser. For example, some browsers may view sessions as limited to tabs within a single window, while others may separate windows into different sessions. Additionally, the browser often provides users with tools for creating and modifying session-related data, and even editing sessions stored on the system's hard drive.

Summary: Session Hijacking Targets Server Sessions

To summarize, while browser sessions are indeed established by the browser, users can manipulate various aspects of these sessions. However, session hijacking primarily targets server-side sessions, involving the manipulation of the session ID exchanged between the client and server.

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