Code injection can occur when using dynamic data in calls to system() and related
Counter Measures
• Limit or remove use of system(), exec(), eval(),back tick(‘), and shell_exec()
• escapeshellarg() to escape arguments
• escapeshellcmd() to escape commands
The PHP option allow_url_include normally allows a programmer to include() a remote file (as PHP code) using a URL rather than a local file path. For security reasons, this feature should be disabled. If a script claims to require this feature, you should look into alternative software, as the use of this feature indicates serious design flaws.
There are a number of reasons why URL includes should always be avoided:
It’s insecure – if your application can be tricked into including content from a URL outside itself (and there are a number of common ways this can happen), an attacker can force your application to start running code from their own web site.
It’s inefficient – if your PHP script includes content from a URL, then the web server must make HTTP requests to generate the page. This makes your page load much slower than necessary, especially if the site you’re loading content from is responding slowly.
It’s unreliable, for the same reasons – if the web server you are loading content from occasionally fails to respond, your web site also sometimes fails to load properly.
It’s usually unnecessary – in most cases, allow_url_include can be avoided either by including the content directly (if it is being loaded from a domain you host) or by loading and printing the content without evaluating it as PHP.
Remote code injections attempt to run the attacker’s code on a server, often by exploiting the functionality of the include or require functions.
The eval(), exec(), system(), and shell_exec() functions are vulnerable to remote code injections.
Include / Require attacks occur when including and executing files (possible from remote servers and includes remote code execution)
Counter Measures
• Check data against a whitelist
• Remove paths using basename()
• Set allow_url_include = off in php.ini that helps somewhat but not sufficient, as some attack vectors remain open
The mysqli_real_escape_string() function escapes special characters in a string for use in an SQL statement
• A request generated from a user’s browser without the user’s knowledge
• Relies on web site trust of logged-in users
• An attack involves tricking a user into transmitting ‘bad’ html with a request, which then returns sensitive data to the attacker
• Executed via iframes, xmlhttprequest calls or embedded in tags such as <script>, <object>, <embed>, <img>, …
Example
<form name="myForm"> <input type="hidden" name="item_id" value="123" /> <input type="hidden" name="quantity" value="1" /> </form> <script>document.forms['myForm'].submit();</script>
Counter Measures
• Use a unique form token in a hidden input field to verify the request
• Require re-login before sensitive operations (ex: financial)
Counter Measures
• Regenerate the session id upon login, before authentication, using session_regenerate_id(true). passing boolean true removes the old session and is critical as a counter measure
• Also, regenerate session id prior to “critical” operations
• Use ssl encryption for the login, or assign a hidden key (not as good)
• Check that the ip address remains the same (although not always reliable)
• Use short session timeout
• Provide user logout
• Destroy an old and create a new session with: session_regenerate_id(true)
• Set php configuration directive session.use_only_cookies = 1
• Prevent javascript access to session cookie with php configuration directive session.cookie_httponly = 1
The configuration directive cgi.force_redirect prevents anyone from calling PHP directly with a URL like http://my.host/cgi-bin/php/secretdir/script.php. Instead, PHP will only parse in this mode if it has gone through a web server redirect rule. PHP older than 4.2.0 used –enable-force-cgi-redirect compile time option for this.
Usually the redirection in the Apache configuration is done with the following directives:
Action php-script /cgi-bin/php AddHandler php-script .php
This option has only been tested with the Apache web server, and relies on Apache to set the non-standard CGI environment variable REDIRECT_STATUS on redirected requests. If your web server does not support any way of telling if the request is direct or redirected, you cannot use this option and you must use one of the other ways of running the CGI version.
session_regenerate_id — Update the current session id with a newly generated one
session_regenerate_id() will replace the current session id with a new one, and keep the current session information.
When session.use_trans_sid is enabled, output must be started after session_regenerate_id() call. Otherwise, old session ID is used.
Example
<?php
session_start();
if (isset($_SESSION['destroyed'])
&& $_SESSION['destroyed'] < time() - 300) {
remove_all_authentication_flag_from_active_sessions($_SESSION['userid']);
throw(new DestroyedSessionAccessException);
}
$old_sessionid = session_id();
$_SESSION['destroyed'] = time();
session_regenerate_id();
unset($_SESSION['destroyed']);
$new_sessionid = session_id();
echo "Old Session: $old_sessionid<br />";
echo "New Session: $new_sessionid<br />";
print_r($_SESSION);
?>
• Combines individual sql operations into one
• Usually start with begin or begin transaction
• Execute the transaction using commit
• Cancel the transaction using rollback
Example
START TRANSACTION; SELECT @A:=SUM(salary) FROM table1 WHERE type=1; UPDATE table2 SET summary=@A WHERE type=1; COMMIT;
Creating a copy of an object with fully replicated properties is not always the wanted behavior. A good example of the need for copy constructors, is if you have an object which represents a GTK window and the object holds the resource of this GTK window, when you create a duplicate you might want to create a new window with the same properties and have the new object hold the resource of the new window. Another example is if your object holds a reference to another object which it uses and when you replicate the parent object you want to create a new instance of this other object so that the replica has its own separate copy.
An object copy is created by using the clone keyword (which calls the object’s __clone() method if possible). An object’s __clone() method cannot be called directly.
$copy_of_object = clone $object;
When an object is cloned, PHP 5 will perform a shallow copy of all of the object’s properties. Any properties that are references to other variables will remain references.