session_regenerate_id

(PHP 4 >= 4.3.2, PHP 5, PHP 7)

session_regenerate_id — 使用新生成的会话 ID 更新现有会话 ID

说明

bool session_regenerate_id ([ bool $delete_old_session = false ] )

session_regenerate_id() 在不修改当前会话中数据的前提下使用新的 ID 替换原有会话 ID。

如果启用了 session.use_trans_sid 选项， 那么必须在调用 session_regenerate_id() 函数之后开始进行输出工作， 否则会导致使用原有的会话 ID。

Warning

当前的 session_regenerate_id 并没有很好的处理在诸如移动数据网络和 WiFi 网络不稳定的场景。 因此，调用 session_regenerate_id 函数 可能会导致会话丢失。

你不应该直接销毁旧的会话所关联的数据， 而是应该使用时间戳机制来控制对于已经失效的会话 ID 的访问。 否则，可能会在并发访问的场景下导致会话数据不一致、 会话丢失等情况，甚至可能引发客户端（浏览器）创建很多无用的会话 ID。 但是，另外一方面来讲，立即删除会话中的数据 可以防止会话劫持攻击。

参数

delete_old_session

是否删除原 ID 所关联的会话存储文件。 如果你需要避免会话并发访问冲突，那么不应该立即删除会话中的数据。 如果你需要防止会话劫持攻击，那么可以立即删除会话数据。

返回值

成功时返回 TRUE， 或者在失败时返回 FALSE。

更新日志

版本 说明
7.0.0 session_regenerate_id() 函数在关闭过期会话之前保存其中的数据。
5.1.0 新加 delete_old_session 参数。
4.3.3 如果启用会话 cookie， 调用 session_regenerate_id() 函数 会使用新的会话 ID 来生成 cookie 并发送给客户端。

范例

Example #1 A session_regenerate_id() 示例

<?php
// 注意：下列不是完整的代码，只是一个示例

session_start();

// 检查会话被销毁的时间戳
if (isset($_SESSION['destroyed'])
    && $_SESSION['destroyed'] < time() - 300) {
    // 通常不会发生这种情况。如果发生，那么可能是由于不稳定的网络状况或者被攻击导致的
    // 移除用户会话中的认证信息
    remove_all_authentication_flag_from_active_sessions($_SESSION['userid']);
    throw(new DestroyedSessionAccessException);
}

$old_sessionid = session_id();

// 设置会话销毁时间戳
$_SESSION['destroyed'] = time(); // 从 PHP 7.0.0 开始, session_regenerate_id() 会自动保存会话数据

// 如果直接调用 session_regenerate_id() 函数可能会导致会话丢失的情况，
// 参见下面的例程
session_regenerate_id();

// 新创建的会话不需要时间戳
unset($_SESSION['destroyed']);

$new_sessionid = session_id();

echo "Old Session: $old_sessionid<br />";
echo "New Session: $new_sessionid<br />";

print_r($_SESSION);
?>

当前的会话模块未能很好的处理在网络不稳定的时候导致会话丢失的场景。 你需要自行管理会话 ID 避免调用 session_regenerate_id 导致会话丢失。

Example #2 Avoiding lost session by session_regenerate_id()

<?php
// 注意：下列不是完整的代码，只是一个示例
// my_session_start() 和 my_session_regenerate_id()
// 函数可以避免在网络不稳定的情况下导致会话丢失的问题。
// 并且还可以避免用户会话被攻击者利用

function my_session_start() {
    session_start();
    if (isset($_SESSION['destroyed'])) {
       if ($_SESSION['destroyed'] < time()-300) {
           // 通常不会发生这种情况。如果发生，那么可能是由于不稳定的网络状况或者被攻击导致的
           // 移除用户会话中的认证信息
           remove_all_authentication_flag_from_active_sessions($_SESSION['userid']);
           throw(new DestroyedSessionAccessException);
       }
       if (isset($_SESSION['new_session_id'])) {
           // 尚未完全过期，可能是由于网络不稳定引起的。
           // 尝试再次设置正确的会话 ID cookie。
           // 注意：如果你需要移除认证标记，那么不要尝试再次设置会话 ID。
           session_commit();
           session_id($_SESSION['new_session_id']);
           // 现在有了新的会话 ID 了。
           session_start();
           return;
       }
   }
}

function my_session_regenerate_id() {
    // 如果由于不稳定的网络导致没有创建会话 ID，
    // 那么就创建一个
    $new_session_id = session_create_id();
    $_SESSION['new_session_id'] = $new_session_id;
    
    // 设置销毁时间戳
    $_SESSION['destroyed'] = time();
    
    // 保存并关闭会话
    session_commit();

    // 使用新的会话 ID 开始会话
    session_id($new_session_id);
    ini_set('session.use_strict_mode', 0);
    session_start();
    ini_set('session.use_strict_mode', 1);
    
    // 新的会话不需要这 2 个数据了
    unset($_SESSION['destroyed']);
    unset($_SESSION['new_session_id']);
}
?>

参见

User Contributed Notes

mikebranttx at gmail dot com 18-May-2017 12:10
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).
k-gun !! mail 09-Jan-2017 08:27
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#119997
ei dot rik dot ops dot tad at gmail dot com 02-Jun-2016 07:11
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.
tedivm at tedivm dot com 18-Jan-2016 05:37
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))
?>
kgm_india at yahoo dot co dot in 25-Nov-2013 08:40
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.
spmtrap at yahoo dot com 31-Jan-2012 11:48
`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`.
gr at gr5 dot org 31-Aug-2011 03:57
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();
?>
Ben Johnson 04-Oct-2010 03:50
To "start a new session", try the following:

<?php
session_start();
session_regenerate_id();
session_destroy();
unset($_SESSION);
session_start();
?>
raido dot aasoja at gmail dot com 27-Sep-2010 08:28
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. :)
tedivm at tedivm dot com 30-Dec-2008 03:36
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;
    }
}

?>
soapergem at gmail dot com 30-Aug-2008 12:50
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.
primenetworkzx at gmail dot com 14-Jun-2008 08:40
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.
sopel 19-Sep-2005 02:32
for php 5.1> user probably worth visiting is http://ilia.ws/archives/47-session_regenerate_id-Improvement.html
dyer85 at gmail dot com 25-Aug-2005 07:59
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.
Nicolas dot Chachereau at Infomaniak dot ch 02-Jun-2005 08:40
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().
chris at knowledge dot tee-vee 17-Jan-2005 02:51
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]
licp at hotmail dot com 07-Jan-2005 05:07
By inspecting the source code, I am not sure that after session_regenerate_id() run, the original session data does not destroy (still keeps at the system) that sniffers still hijack by applying original session identifier.

In addition, I find that if user-level session storage handler is used. session_regenerate_id() does not work.
php at cny dot de 20-Dec-2004 06:08
Also note that REMOTE_ADDR may change on every request if the user comes through a proxy farm. Most AOL-users do.
ross at kndr dot org 16-Nov-2004 12:41
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.
elger at NOSPAM dot yellowbee dot nl 28-Oct-2004 11:10
Take good notice of the new cookie being sent on calling session_regenerate_id on cookie-enabled sessions.
Make sure your page is reloaded otherwise you'll get an "session_destroy(): Session object destruction failed" error. So here are the examples:

Wrong:
<?php
    session_start();
    session_regenerate_id();
    session_destroy();
?>

Correct-like:
<?php
if (!$_GET['mode']){
    session_start();
    session_regenerate_id();
    header('location: '.$_SERVER['REQUEST_URI'].'?mode=destroy');
} else {
    session_start();
    session_destroy();
}
?>

I noted this because googleing on the previous mentioned error leads to all kinds of bug reports, but not to the solution. (which is, of course, to read the manual)
babel at nosqamplease sympatico ca 23-Feb-2004 05:48
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.
php at 5mm de 05-Sep-2003 03:01
This feature seems to create a new session ID without clearing the old session data. This is a very important feature for security validation:

$usedns = TRUE; // for eliminating failture by proxys using IP chains, but slower

$useragent = getenv("HTTP_USER_AGENT");
$host = getenv("REMOTE_ADDR");
$dns = $global['dns'] ? @gethostbyaddr($host):$host;

session_start();

if(session_is_registered('securitycheck')) {
    if(
            (($_SESSION['session']['host'] != $this->host) && !$usedns)
         || ($_SESSION['session']['dns'] != $this->dns)
         || ($_SESSION['session']['useragent'] != $this->useragent)
    ) {
        session_regenerate_id();
        session_unset();
    }
} else {
    $currentdata = array();
    $currentdata['host'] = $this->host;
    $currentdata['dns'] = $this->dns;
    $currentdata['useragent'] = $this->useragent;
   
    session_register('securitycheck', $currentdata);
}

If sombody steals an active SID (e.g. by referrer or injection attack), he can?t be validated because of either the host / dns or useragent and will get a new (empty) SID, without interrupting the original session.

Please mail me for any comments: php at 5mm de
madsen at sjovedyr.dk 28-Aug-2003 04:26
I 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.