(PHP 4 >= 4.3.2, PHP 5, PHP 7, PHP 8)
session_regenerate_id — Ersetzt die aktuelle Session-ID durch eine neu erzeugte
Die Funktion session_regenerate_id() ersetzt die aktuelle Session-ID durch eine neue und übernimmt die aktuellen Session-Informationen.
Wenn session.use_trans_sid aktiviert ist, darf die Ausgabe erst nach dem Aufruf von session_regenerate_id() beginnen. Andernfalls wird die alte Session-ID verwendet.
Zurzeit kann session_regenerate_id nicht gut mit unstabilen Netzwerken, z. B. Mobil- und WiFi-Netzwerke, umgehen. Daher kann es zu verlorenen Sessions kommen, wenn session_regenerate_id aufgerufen wird.
Die alten Session-Daten sollten nicht sofort zerstört werden, sondern es sollte ein Destroy-Zeitstempel verwendet werden und der Zugriff auf die alte Session-ID sollte kontrolliert werden. Andernfalls kann ein konkurrierender Zugriff auf die Seite möglicherweise zu einem inkonsistenten Zustand führen, oder die Session kann gänzlich verloren werden, oder es kann sich eine Race-Condition im Client (Browser) ergeben und viele Session-IDs könnten nutzlos erzeugt werden. Die sofortige Löschung der Session-Daten verhindert die Erkennung von Session-Hijack-Angriffen und auch deren Vorbeugung.
delete_old_sessionLegt fest, ob die zugehörige alte Session-Datei gelöscht werden soll oder nicht. Die alten Session-Daten sollten nicht gelöscht werden, wenn Race-Conditions, die durch die Löschung verursacht werden, verhindert, oder Session-Hijack-Angriffe erkannt oder vermieden werden müssen.
Beispiel #1 Ein session_regenerate_id()-Beispiel
<?php
// ACHTUNG: dieser Code ist nicht voll funktionsfähig, sondern dient nur als Beispiel!
session_start();
// Prüfe den Destroy-Zeitstempel
if (isset($_SESSION['destroyed'])
&& $_SESSION['destroyed'] < time() - 300) {
// Dies sollte normalerweise nicht passieren. Es könnte durch einen Angriff
// oder ein unstabiles Netzwerk verursacht worden sein.
// Entferne den Authentifizierungsstatus dieser Nutzer-Session.
remove_all_authentication_flag_from_active_sessions($_SESSION['userid']);
throw(new DestroyedSessionAccessException);
}
$old_sessionid = session_id();
// Lege den Destroy-Zeitstempel fest
$_SESSION['destroyed'] = time(); // session_regenerate_id() speichert die
// alten Session-Daten
// Der einfache Aufruf von session_regenerate_id() kann in einer verlorenen
// Session resultieren, etc. Siehe das nächste Beispiel.
session_regenerate_id();
// Die neue Session braucht keinen Destroy-Zeitstempel
unset($_SESSION['destroyed']);
$new_sessionid = session_id();
echo "Alte Session: $old_sessionid<br />";
echo "Neue Session: $new_sessionid<br />";
print_r($_SESSION);
?>Zurzeit kann das Session-Modul nicht gut mit unstabilen Netzwerken umgehen. Die Session-ID sollte selbst verwaltet werden, um verlorene Sessions durch session_regenarate_id zu verhindern.
Beispiel #2 Verhindern von verlorenen Sessions durch session_regenerate_id()
<?php
// ACHTUNG: dieser Code ist nicht voll funktionsfähig, sondern dient nur als Beispiel!
// my_session_start() und my_session_regenerate_id() verhindern verlorene Session
// durch unstabile Netzwerke. Zusätzlich kann dieser Code dem Ausnutzen einer
// gestohlenen Session durch Angreifer vorbeugen.
function my_session_start() {
session_start();
if (isset($_SESSION['destroyed'])) {
if ($_SESSION['destroyed'] < time()-300) {
// Dies sollte normalerweise nicht passieren. Es könnte durch einen Angriff
// oder ein unstabiles Netzwerk verursacht worden sein.
// Entferne den Authentifizierungsstatus dieser Nutzer-Session.
remove_all_authentication_flag_from_active_sessions($_SESSION['userid']);
throw(new DestroyedSessionAccessException);
}
if (isset($_SESSION['new_session_id'])) {
// Noch nicht vollständig abgelaufen. Könnte an einem verlorenen Cookie
// durch ein unstabiles Netzwerk liegen.
// Noch einmal versuchen, das ordnungsgemäße Session-ID-Cookie zu setzen.
// ACHTUNG: es sollte nicht versucht werden, die Session-ID erneut
// festzulegen, wenn das Authentifizierungsflag entfernt werden soll.
session_commit();
session_id($_SESSION['new_session_id']);
// Die neue Session-ID sollte existieren
session_start();
return;
}
}
}
function my_session_regenerate_id() {
// Eine neue Session-ID wird benötigt, um die richtige Session-ID festzulegen,
// wenn die Session-ID aufgrund eines unstabilen Netzwerks nicht gesetzt wurde.
$new_session_id = session_create_id();
$_SESSION['new_session_id'] = $new_session_id;
// Lege den Destroy-Zeitstempel fest
$_SESSION['destroyed'] = time();
// Schreibe und schließe die aktuelle Session
session_commit();
// Starte die Session mit einer neuen Session-ID
session_id($new_session_id);
ini_set('session.use_strict_mode', 0);
session_start();
ini_set('session.use_strict_mode', 1);
// Die neue Session braucht sie nicht
unset($_SESSION['destroyed']);
unset($_SESSION['new_session_id']);
}
?>
I wrote the current top voted comment on this and wanted to add something. The existing code from my previous comment generates it's nonces in an insecure way-
<?php
$_SESSION['nonce'] = md5(microtime(true));
?>
Since "microtime" is predictable it makes brute forcing the nonce much easier. A better option would be something that utilizes randomness, such as-
<?php
bin2hex(openssl_random_pseudo_bytes(32))
?>I wrote the following code for a project I'm working on- it attempts to resolve the regenerate issue, as well as deal with a couple of other session related things.
I tried to make it a little more generic and usable (for instance, in the full version it throws different types of exceptions for the different types of session issues), so hopefully someone might find it useful.
<?php
function regenerateSession($reload = false)
{
// This token is used by forms to prevent cross site forgery attempts
if(!isset($_SESSION['nonce']) || $reload)
$_SESSION['nonce'] = md5(microtime(true));
if(!isset($_SESSION['IPaddress']) || $reload)
$_SESSION['IPaddress'] = $_SERVER['REMOTE_ADDR'];
if(!isset($_SESSION['userAgent']) || $reload)
$_SESSION['userAgent'] = $_SERVER['HTTP_USER_AGENT'];
//$_SESSION['user_id'] = $this->user->getId();
// Set current session to expire in 1 minute
$_SESSION['OBSOLETE'] = true;
$_SESSION['EXPIRES'] = time() + 60;
// Create new session without destroying the old one
session_regenerate_id(false);
// Grab current session ID and close both sessions to allow other scripts to use them
$newSession = session_id();
session_write_close();
// Set session ID to the new one, and start it back up again
session_id($newSession);
session_start();
// Don't want this one to expire
unset($_SESSION['OBSOLETE']);
unset($_SESSION['EXPIRES']);
}
function checkSession()
{
try{
if($_SESSION['OBSOLETE'] && ($_SESSION['EXPIRES'] < time()))
throw new Exception('Attempt to use expired session.');
if(!is_numeric($_SESSION['user_id']))
throw new Exception('No session started.');
if($_SESSION['IPaddress'] != $_SERVER['REMOTE_ADDR'])
throw new Exception('IP Address mixmatch (possible session hijacking attempt).');
if($_SESSION['userAgent'] != $_SERVER['HTTP_USER_AGENT'])
throw new Exception('Useragent mixmatch (possible session hijacking attempt).');
if(!$this->loadUser($_SESSION['user_id']))
throw new Exception('Attempted to log in user that does not exist with ID: ' . $_SESSION['user_id']);
if(!$_SESSION['OBSOLETE'] && mt_rand(1, 100) == 1)
{
$this->regenerateSession();
}
return true;
}catch(Exception $e){
return false;
}
}
?>In PHP 5.6 (and probably older versions), session_regenerate_id(true) do not trigger a read() call to the session handler for the new session id.
In PHP 7, read() is triggered during session_regenerate_id(true). Nice to know when working with custom session handlers.If you are trying to maintain 2 active sessions don't use session_regenerate_id(). Especially if the first session is closed and it's time to open the second. Because the session id is cached you also have to explicitly set it the second time.
<?php
session_name('PHPSESSID'); // redundant - here for clarity
session_start();
// ...do stuff
session_write_close();
// now switch to session 2...
session_name('PHPSESSID_2');
if (isset($_COOKIE['phpsessid_2']))
session_id($_COOKIE['phpsessid_2']); // not doing this will simply reopen the first session again
else
session_id(sha1(mt_rand()); // dont use session_regenerate_id() here. Not creating a new id will create two cookies with same session id and same session variables
session_start();
// ... do stuff with session 2
session_write_close();
?>In a previous note, php at 5mm de describes how to prevent session hijacking by
ensuring that the session id provided matches the HTTP_USER_AGENT and REMOTE_ADDR fields that were present when the session id was first issued. It should be noted that HTTP_USER_AGENT is supplied by the client, and so can be easily modified by a malicious user. Also, the client IP addresses can be spoofed, although that's a bit more difficult. Care should be taken when relying on the session for authentication.`session_regenerate_id` sends a new cookie but doesn't overwrite the value stored in `$_COOKIE`. After calling `session_destroy`, the open session ID is discarded, so simply restarting the session with `session_start` (as done in Ben Johnson's code) will re-open the original, though now empty, session for the current request (subsequent requests will use the new session ID). Instead of `session_destroy`+`session_start`, use the `$delete_old_session` parameter to `session_regenerate_id` to delete the previous session data.
<?php
session_start();
/* Create a new session, deleting the previous session data. */
session_regenerate_id(TRUE);
/* erase data carried over from previous session */
$_SESSION=array();
?>
To start a new session and leave the old untouched, simply leave out the argument to `session_regenerate_id`.Also note that REMOTE_ADDR may change on every request if the user comes through a proxy farm. Most AOL-users do.To add to php at 5mm de's comments:
If the session is held over https, it's even better to save the client's cert or ssl session id instead of the hostname or ip, as it's proxy-transparent and more secure.Document example is wrong with usage of "session.use_strict_mode" according to RFC (says: "warning error for session_id() when use_strice_mode=1" on https://wiki.php.net/rfc/strict_sessions).
So, this directive affects "session_id()" not "session_start()". So usage must be like this;
<?php
// first set ini
ini_set('session.use_strict_mode', '0');
// and
session_id($sid);
// then
// maybe run this: ini_restore('session.use_strict_mode');
// then go on...
?>
Refs (ctrl+f & use_strict_mode);
https://wiki.php.net/rfc/strict_sessions
https://wiki.php.net/rfc/session-create-id
http://php.net/manual/en/function.session-id.php#119997I had problems with a proxy changing a visitors session_id-cookie, so he'd get a LOT of errors when visiting my site.
I handled the bogus session-id's like this. (Note: It only works in versions > 4.3.2.)
<?php
// Start a session and suppress error-messages.
@session_start();
// Catch bogus session-id's.
if (!preg_match("/^[0-9a-z]*$/i", session_id())) {
// Output a warning about the messed up session-id.
$error->handleError("WARN", "Your session id is messed up, you might not be able to use some features on this site.");
// Generate a fresh session-id.
session_regenerate_id();
}
// Site contents.
?>
Hope someone can use it.Session_destroy() does not only destroy the data associated with the current session_id (i.e. the file if you use the default session save handler), but also the session itself: if you call session_destroy() and then session_regenerate_id(), it will return false, and session_id() won't return anything. In order to manipulate a session after destroying it, you need to restart it.
So in fact, the code mentionned by chris won't work. If you want to destroy the file associated with the old session_id, try the following:
<?php
session_start();
$old_sessid = session_id();
session_regenerate_id();
$new_sessid = session_id();
session_id($old_sessid);
session_destroy();
//If you don't copy the $_SESSION array, you won't be able to use the data associated with the old session id.
$old_session = $_SESSION;
session_id($new_sessid);
session_start();
$_SESSION = $old_session;
//...
?>
Note: this technique will send 3 Set-Cookie headers (one on each session_start() and one on session_regenerate_id()). I don't think this is a problem, but if it appears to be one, you could either leave it alone and wait for the garbage collector to catch the file associated with the old session, or try to delete the file with unlink().The code example provided of my_session_regenerate_id() DOES NOT work and DESTROYS all session variables. Plus the second ini_set gives an error.
The code for regenerating (only that part, the rest seems fine) should simply be this:
<?php
function my_session_regenerate_id() {
$new_session_id = session_create_id();
// backup session variables
$keepSession = $_SESSION ;
// add info for users with bad connection not receiving the new session id
$_SESSION['new_session_id'] = $new_session_id;
// Set destroy timestamp
$_SESSION['destroyed'] = time();
// Write and close current session;
session_commit() ;
// Start session with new session ID
ini_set('session.use_strict_mode', 0);
session_id($new_session_id);
session_start();
$_SESSION = $keepSession ;
}
?>This can be a very dangerous function if you're not careful about how you handle things, because even though it generates a whole new set of session data, it keeps the old data "open" until the script terminates, locking out any other scripts trying to run concurrently with the old session id.
Recently I came across a situation where I wanted to explicitly pass in a session ID, copy the data from that session into a *new* session, and then continue operating under that new session, thereby allowing other scripts to use the old one concurrently. But I quickly found that these "other scripts" would not execute until the first script finished--even though it had already started a new session--because it kept the old session open.
So if you're trying to copy over session data to a new session to free up the old session for continued, concurrent use, here's some code to ensure nobody's feet get stepped on:
<?php
// get session id of an existing session
$sid = $_GET['sid'];
// start the old session to retrieve $_SESSION data
session_id($sid);
session_start();
// start a new session; this copies the $_SESSION data over
session_regenerate_id();
// hang on to the new session id
$sid = session_id();
// close the old and new sessions
session_write_close();
// re-open the new session
session_id($sid);
session_start();
/* main code here */
?>
This could probably be encapsulated into a function with one parameter as well to save space if it was a repeated thing.If you are storing your session data in a database you have to manually update the session_id in the database. The session_set_save_handler() will not do it for you.
function UpdateSessID() {
$old_sess_id = session_id();
session_regenerate_id(false);
$new_sess_id = session_id();
$query = "UPDATE `session_table` SET `session_id` = '$new_sess_id' WHERE session_id = '$old_sess_id'";
mysql_query($query);
}
Be sure to set session_regenerate_id() to FALSE since it's not really necessary to delete the whole record from MySQL and add it again. That's unnecessary overhead. Only changing the id matters.There could be a potential problem with elger at NOSPAM dot yellowbee dot nl's a few posts below. In the code, was used the REQUEST_URI server variable, which, in some cases might already contain the query string. Therefore, always apending '?whatever=foo' would occasionally cause the script to malfunction. I suggest using PHP_SELF, which will not contain the query string after the file.Note that in current PHP 7.2 nightly builds example #2 above will not work as shown. You will get following error upon trying to turn strict mode back on after session_start():
"ini_set(): A session is active. You cannot change the session module's ini settings at this time"
I suppose this means that for any session where you perform session ID regeneration or session ID forwarding (from a session for which a recent session ID regeneration was performed to the new session ID). That you will just have to live with strict mode being disabled for the remainder of that active session.
I don't know that this is really a security concern so long as you are following a single-session per request design (i.e. you are not working with multiple concurrent sessions).licp - no, session_regenerate_id() does not destroy any saved session data.
elger, I prefer the following order
[code]
// populate $_SESSION with any previously saved session data for the current session_id
session_start();
...
// delete any saved data associated with current session_id, $_SESSION is not changed
session_destroy();
// change session_id, $_SESSION not altered
session_regenerate_id();
...
// save any $_SESSION data under the current session_id
session_close();
[/code]<?php
function my_session_regenerate_id() {
...
session_start();
...
unset($_SESSION['destroyed']);
unset($_SESSION['new_session_id']);
}
?>
Within my_session_regenerate_id(), unset($_SESSION['destroyed']) and
unset($_SESSION['new_session_id']) are useless because session_start() will open an empty session. They would be needed if built-in session_regenerate_id() was called.as far as I have understood reading this online notes,
session_name() is the name which is identified as session a through the cookies or http links.
session_id is like a transaction within a session_name() and one session_name may have many session_id
each session_id has the corresponding data stored.
session_id are used in read and write callback under a session_name
whatever it is, first call the
session_name(),
then call session_id ()
and then call start_session()
start_session will open the session_name, then check the session_id called before and use it in the read or write call back for storing or retrieving data
calling start_session() without session_name or session_id will use the default session_name and the default session_id in that order
I hope if the order is followed there should not be any problems.
do not call session_name or session_id after start_session(), if you are specific on using them.
thank you for others note.A note on lost sessions and trying to fix it with session_regenerate_id:
Make sure that you're not trying to push SimpleXML object to the session. It just won't go without first converting it to array. :)for php 5.1> user probably worth visiting is http://ilia.ws/archives/47-session_regenerate_id-Improvement.html