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Session fixation attack12/30/2023 ![]() Basically, when the session starts, store it in something like $_SESSION. Include the user's IP address from $_SERVER in the session. Note that this can be faked so it's not 100% reliable, but it's better than not. Then, on each subsequent request check that it matches. Include the user agent from $_SERVER in the session. You want to change this often since if an attacker does hijack a session you don't want them to be able to use it for too long. I wouldn't do this every request (unless you really need that level of security), but at a random interval. But depending on your use-case, it may be an option. If you're really paranoid you could rotate the session name too, but beware that all sessions will automatically be invalidated if you change this (for example, if you make it dependent on the time). This is accomplished by calling session_name() with your own identifier name as the first parameter prior to calling session_start. Set the former to session.entropy_file = /dev/urandom and the latter to the number of bytes that will be read from the entropy file, for example session.entropy_length = 256.Ĭhange the name of the session from the default PHPSESSID. Set an additional entropy with session.entropy_file and session.entropy_length in your php.ini file. The ID will be shorter, but uses more characters. While this doesn't make it any harder to crack, it does make a difference when the attacker tries to guess the session identifier. Set this to session.hash_bits_per_character = 5. Send a strong hash: session.hash_bits_per_character in php.ini. If PHP = 5.3, set it to session.hash_function = sha256 or session.hash_function = sha512. Use a strong session hash identifier: session.hash_function in php.ini. You can however put steps in to make it very difficult and harder to use. You cannot directly prevent session hijacking. That means that since the attacker has the identifier, they are all but indistinguishable from the valid user with respect to the server. This is where an attacker gets a hold of a session identifier and is able to send requests as if they were that user. Regenerate the session ID anytime the session's status changes. This will tell PHP to never use URLs with session identifiers. ![]() Set e_only_cookies = 1 in your php.ini file. This will tell PHP not to include the identifier in the URL, and not to read the URL for identifiers. Set e_trans_sid = 0 in your php.ini file. There are a few ways to prevent session fixation (do all of them): Once the attacker gives the url to the client, the attack is the same as a session hijacking attack. ![]() Typically in PHP it's done by giving them a url like. This is where an attacker explicitly sets the session identifier of a session for a user. Anything that does not require some form of extra authentications such as retyping your password.Ok, there are two separate but related problems, and each is handled differently. This means that she can do anything the victim could do on the site - create and delete content, edit profiles, whatever. Since the attacker knows the session ID, she can now use it to impersonate the victim. When the victim loggs in, the session ID in question goes from not being associated with any user to being associated with the victim. When the victim logs into the website, what can an attacker do with it? Any examples? It would be foolish by the attacker to send a session ID for a session where she is logged in as herself, since that would give the victim control over the attackers account! So the attacker never logs in on the site. for an actual session that is not logged in, so it is not yet associated with any user.just a random number on the right format, or not at all registered at the server - i.e. ![]() The attacker would send a link with a session ID that is either: When the attacker uses an already existing session ID, doesn't the server know that the session id has already been taken by the attacker? ![]()
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