ADS - GoldenWeb.it Directory "Premium" Links

Hotel Ischia - Scegli Ischiaprenota.com
Cerchi un hotel Ischia? Su Ischiaprenota.com tantissime offerte hotel e lastminute Ischia a prezzi imbattibili. Hotel 3,4 e 5 stelle a partire da 20 a notte. Trattamento All-Inclusive, Pensione completa, Mezza Pensione e solo pernottamento. Nessun anticipo, paghi direttamente in hotel. Assistenza con personale Ischitano.
Dentista low cost sociale
Ti piacerebbe tornare a sorridere? Vuoi dei nuovi denti su Impianti dentali a prezzi estremamente contenuti? Ora puoi realizzare il tuo sogno! Du.Val., in collaborazione con un'importante azienda produttrice di impianti dentali in Italia registrata nel repertorio dei dispositivi medici del Ministero della Salute, ti offre una protesi fissa su impianti / impianti dentali a prezzi sociali estremamente contenuti direttamente presso lo studio collaboratore a Milano: impianti dentali made in Italy
Adriana Online
Adriana Online è un ecommerce differente dai soliti siti di vendita online di abbigliamento. Lo stile che si ricerca è per una donna che vuole essere sempre di tendenza ma con uno spirito unico, come unici sono i brand inseriti nel catalogo online sempre aggiornato
Assistenza Caldaie Roma Indipendent
Offre un servizio di assistenza caldaie a roma e provincia.

Submit Your Link...

PHP manual


Filesystem Security

Table of Contents

PHP is subject to the security built into most server systems with respect to permissions on a file and directory basis. This allows you to control which files in the filesystem may be read. Care should be taken with any files which are world readable to ensure that they are safe for reading by all users who have access to that filesystem.

Since PHP was designed to allow user level access to the filesystem, it's entirely possible to write a PHP script that will allow you to read system files such as /etc/passwd, modify your ethernet connections, send massive printer jobs out, etc. This has some obvious implications, in that you need to ensure that the files that you read from and write to are the appropriate ones.

Consider the following script, where a user indicates that they'd like to delete a file in their home directory. This assumes a situation where a PHP web interface is regularly used for file management, so the Apache user is allowed to delete files in the user home directories.

Example #1 Poor variable checking leads to....

<?php
// remove a file from the user's home directory
$username $_POST['user_submitted_name'];
$userfile $_POST['user_submitted_filename'];
$homedir  "/home/$username";

unlink("$homedir/$userfile");

echo 
"The file has been deleted!";
?>
Since the username and the filename are postable from a user form, they can submit a username and a filename belonging to someone else, and delete it even if they're not supposed to be allowed to do so. In this case, you'd want to use some other form of authentication. Consider what could happen if the variables submitted were "../etc/" and "passwd". The code would then effectively read:

Example #2 ... A filesystem attack

<?php
// removes a file from anywhere on the hard drive that
// the PHP user has access to. If PHP has root access:
$username $_POST['user_submitted_name']; // "../etc"
$userfile $_POST['user_submitted_filename']; // "passwd"
$homedir  "/home/$username"// "/home/../etc"

unlink("$homedir/$userfile"); // "/home/../etc/passwd"

echo "The file has been deleted!";
?>
There are two important measures you should take to prevent these issues.
  • Only allow limited permissions to the PHP web user binary.
  • Check all variables which are submitted.
Here is an improved script:

Example #3 More secure file name checking

<?php
// removes a file from the hard drive that
// the PHP user has access to.
$username $_SERVER['REMOTE_USER']; // using an authentication mechanisim
$userfile basename($_POST['user_submitted_filename']);
$homedir  "/home/$username";

$filepath "$homedir/$userfile";

if (
file_exists($filepath) && unlink($filepath)) {
    
$logstring "Deleted $filepathn";
} else {
    
$logstring "Failed to delete $filepathn";
}
$fp fopen("/home/logging/filedelete.log""a");
fwrite($fp$logstring);
fclose($fp);

echo 
htmlentities($logstringENT_QUOTES);

?>
However, even this is not without its flaws. If your authentication system allowed users to create their own user logins, and a user chose the login "../etc/", the system is once again exposed. For this reason, you may prefer to write a more customized check:

Example #4 More secure file name checking

<?php
$username     
$_SERVER['REMOTE_USER']; // using an authentication mechanisim
$userfile     $_POST['user_submitted_filename'];
$homedir      "/home/$username";

$filepath     "$homedir/$userfile";

if (!
ctype_alnum($username) || !preg_match('/^(?:[a-z0-9_-]|.(?!.))+$/iD'$userfile)) {
    die(
"Bad username/filename");
}

//etc...
?>

Depending on your operating system, there are a wide variety of files which you should be concerned about, including device entries (/dev/ or COM1), configuration files (/etc/ files and the .ini files), well known file storage areas (/home/, My Documents), etc. For this reason, it's usually easier to create a policy where you forbid everything except for what you explicitly allow.