Complete explanation of PHP vulnerabilities (7)-Session hijacking

The server and client communicate through sessions. When the client's browser connects to the server, the server will establish a session for the user. Each user's session is independent and maintained by the server. Each user's session is identified by a unique string, called a session id. When a user makes a request, the http header sent contains the value of session id. The server uses the session id in the http header to identify which user submitted the request.

Session saves the personal data of each user. General web applications will use session to save authenticated user accounts and passwords. When converting different web pages, if you need to verify the user's identity, use the account number and password saved in the session to compare. The life cycle of the session starts when the user connects to the server and ends when the user closes the browser or logs out when the session_destroy function deletes the session data. If the user does not use the computer within 20 minutes, the session will automatically end.

PHP application architecture for processing sessions

Session hijacking

Session hijacking refers to the attacker using various means to obtain the session id of the target user. Once the session ID is obtained, the attacker can use the target user's identity to log in to the website and obtain the target user's operation permissions.

Methods for attackers to obtain the target user’s session ID:

1) Brute force cracking: try various session IDs until they are cracked.

2) Calculation: If the session id is generated in a non-random way, it is possible to calculate it

3) Stealing: Use network interception, xss attacks and other methods to obtain

Session hijacking attack steps

Instances

//login.php session_start(); if (isset($_POST["login"])) { $link = mysql_connect("localhost", "root", "root") or die("无法建立MySQL数据库连接：" . mysql_error()); mysql_select_db("cms") or die("无法选择MySQL数据库"); if (!get_magic_quotes_gpc()) { $query = "select * from member where username=’" . addslashes($_POST["username"]) . "’ and password=’" . addslashes($_POST["password"]) . "’"; } else { $query = "select * from member where username=’" . $_POST["username"] . "’ and password=’" . $_POST["password"] . "’"; } $result = mysql_query($query) or die("执行MySQL查询语句失败：" . mysql_error()); $match_count = mysql_num_rows($result); if ($match_count) { $_SESSION["book"] = 1; mysql_close($link); header("Location: http://localhost/index.php?user=" . $_POST["username"]); } ….. // 打开Session 访客的 Session ID 是：echo session_id(); ?>

After logging in, it will show

Start attacking

//attack.php
php
//Open Session
session_start();
echo "Session of the target user" The ID is: ". session_id() . "
";
echo "The username of the target user is:" . $_SESSION["username"] . "
";
echo "The password of the target user is: " . $_SESSION["password"] . "
";
// Set the number of books to 2000
$_SESSION["book"] = 2000;
?>

Submit http://localhost/attack.php?PHPSESSID=5a6kqe7cufhstuhcmhgr9nsg45 This ID is the obtained customer session id. After refreshing the customer page

session fixed attack

Hackers can use the method of sending the session id to the user to Complete the attack

http://localhost/index.php?user=dodo&PHPSESSID=1234 Send this link to the user dodo for display

Then the attacker visits http://localhost/attack.php ?PHPSESSID=1234, the customer page refreshed and found

Prevention methods

1) Regularly change the session id

Function bool session_regenerate_id([bool delete_old_session])

delete_old_session If true, the old session file will be deleted; if it is false, the old session will be retained. The default is false. Optional

Add

session_start();

session_regenerate_id(TRUE);

...

This way a new session id will be generated every time it is reloaded

2) Changes The name of the session

The default name of the session is PHPSESSID. This variable will be saved in the cookie. If the hacker does not capture the packet and analyze it, he cannot guess the name and block some attacks

session_start();

session_name( "mysessionid");

......

3) Turn off transparent session id

Transparent session id means that when the http request in the browser does not use cookies to formulate the session id, the sessioin id is passed using a link; open php .ini, edit

session.use_trans_sid = 0

In the code

int_set("session.use_trans_sid", 0);

session_start();

...

4) Only check the session from the cookie id

session.use_cookies = 1 means using cookies to store session id

session.use_only_cookies = 1 means only using cookies to store session id, which can avoid session fixation attacks

In the code

int_set("session.use_cookies", 1 );

int_set("session.use_only_cookies", 1); p>

5) Use URL to pass hidden parameters

session_start();

$seid = md5(uniqid(rand()), TRUE ));

$_SESSION["seid"] = $seid;

Although the attacker can obtain the session data, he cannot know the value of $seid. As long as he checks the value of seid, he can confirm whether the current page is a web program. Called by yourself.

The above is the complete solution to PHP vulnerabilities (7) - Session hijacking. For more related content, please pay attention to the PHP Chinese website (m.sbmmt.com)!