mysql_real_escape_string
(PHP 4 >= 4.3.0, PHP 5)
mysql_real_escape_string — Escapes special characters in a string for use in an SQL statement
This extension is deprecated as of PHP 5.5.0, and will be removed in the future. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information. Alternatives to this function include:
Description
$unescaped_string
[, resource $link_identifier = NULL
] )
Escapes special characters in the unescaped_string,
taking into account the current character set of the connection so that it
is safe to place it in a mysql_query(). If binary data
is to be inserted, this function must be used.
mysql_real_escape_string() calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: \x00, \n, \r, \, ', " and \x1a.
This function must always (with few exceptions) be used to make data safe before sending a query to MySQL.
Security: the default character set
The character set must be set either at the server level, or with the API function mysql_set_charset() for it to affect mysql_real_escape_string(). See the concepts section on character sets for more information.
Parameters
-
unescaped_string -
The string that is to be escaped.
-
link_identifier -
The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If no connection is found or established, an
E_WARNINGlevel error is generated.
Return Values
Returns the escaped string, or FALSE on error.
Examples
Example #1 Simple mysql_real_escape_string() example
<?php
// Connect
$link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')
OR die(mysql_error());
// Query
$query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",
mysql_real_escape_string($user),
mysql_real_escape_string($password));
?>
Example #2 An example SQL Injection Attack
<?php
// We didn't check $_POST['password'], it could be anything the user wanted! For example:
$_POST['username'] = 'aidan';
$_POST['password'] = "' OR ''='";
// Query database to check if there are any matching users
$query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'";
mysql_query($query);
// This means the query sent to MySQL would be:
echo $query;
?>
The query sent to MySQL:
SELECT * FROM users WHERE user='aidan' AND password='' OR ''=''
This would allow anyone to log in without a valid password.
Notes
Note:
A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level
E_WARNINGis generated, andFALSEis returned. Iflink_identifierisn't defined, the last MySQL connection is used.
Note:
If magic_quotes_gpc is enabled, first apply stripslashes() to the data. Using this function on data which has already been escaped will escape the data twice.
Note:
If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.
Note: mysql_real_escape_string() does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.
See Also
- mysql_set_charset() - Sets the client character set
- mysql_client_encoding() - Returns the name of the character set
- addslashes() - Quote string with slashes
- stripslashes() - Un-quotes a quoted string
- The magic_quotes_gpc directive
- The magic_quotes_runtime directive
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Коментарии
Note that mysql_real_escape_string doesn't prepend backslashes to \x00, \n, \r, and and \x1a as mentionned in the documentation, but actually replaces the character with a MySQL acceptable representation for queries (e.g. \n is replaced with the '\n' litteral). (\, ', and " are escaped as documented) This doesn't change how you should use this function, but I think it's good to know.There's an interesting quirk in the example #2 about SQL injection: AND takes priority over OR, so the injected query actually executes as WHERE (user='aidan' AND password='') OR ''='', so instead of returning a database record corresponding to an arbitrary username (in this case 'aidan'), it would actually return ALL database records. In no particular order. So an attacker might be able to log in as any account, but not necessarily with any control over which account it is.
Of course a potential attacker could simply modify their parameters to target specific users of interest:
<?php
// E.g. attacker's values
$_POST['username'] = '';
$_POST['password'] = "' OR user = 'administrator' AND '' = '";
// Malformed query
$query = "SELECT * FROM users WHERE user='$_POST[username]' AND password='$_POST[password]'";
echo $query;
// The query sent to MySQL would read:
// SELECT * FROM users WHERE user='' AND password='' OR user='administrator' AND ''='';
// which would allow anyone to gain access to the account named 'administrator'
?>
Just a little function which mimics the original mysql_real_escape_string but which doesn't need an active mysql connection. Could be implemented as a static function in a database class. Hope it helps someone.
<?php
function mysql_escape_mimic($inp) {
if(is_array($inp))
return array_map(__METHOD__, $inp);
if(!empty($inp) && is_string($inp)) {
return str_replace(array('\\', "\0", "\n", "\r", "'", '"', "\x1a"), array('\\\\', '\\0', '\\n', '\\r', "\\'", '\\"', '\\Z'), $inp);
}
return $inp;
}
?>
For further information:http://dev.mysql.com/doc/refman/5.5/en/mysql-real-escape-string.html
(replace your MySQL version in the URL)
No discussion of escaping is complete without telling everyone that you should basically never use external input to generate interpreted code. This goes for SQL statements, or anything you would call any sort of "eval" function on.
So, instead of using this terribly broken function, use parametric prepared statements instead.
Honestly, using user provided data to compose SQL statements should be considered professional negligence and you should be held accountable by your employer or client for not using parametric prepared statements.
What does that mean?
It means instead of building a SQL statement like this:
"INSERT INTO X (A) VALUES(".$_POST["a"].")"
You should use mysqli's prepare() function (mysqli.prepare) to execute a statement that looks like this:
"INSERT INTO X (A) VALUES(?)"
NB: This doesn't mean you should never generate dynamic SQL statements. What it means is that you should never use user-provided data to generate those statements. Any user-provided data should be passed through as parameters to the statement after it has been prepared.
So, for example, if you are building up a little framework and want to do an insert to a table based on the request URI, it's in your best interest to not take the $_SERVER['REQUEST_URI'] value (or any part of it) and directly concatenate that with your query. Instead, you should parse out the portion of the $_SERVER['REQUEST_URI'] value that you want, and map that through some kind of function or associative array to a non-user provided value. If the mapping produces no value, you know that something is wrong with the user provided data.
Failing to follow this has been the cause of a number of SQL-injection problems in the Ruby On Rails framework, even though it uses parametric prepared statements. This is how GitHub was hacked at one point. So, no language is immune to this problem. That's why this is a general best practice and not something specific to PHP and why you should REALLY adopt it.
Also, you should still do some kind of validation of the data provided by users, even when using parametric prepared statements. This is because that user-provided data will often become part of some generated HTML, and you want to ensure that the user provided data isn't going to cause security problems in the browser.
There is requirement for old projects which are using `mysql_escape_string`, and upgrading the PHP version to 7 and above. Basically this happens in maintenance projects where we don't know how many files the functions are used in application. We can use [mysqli.real-escape-string][1] for the function:
If you have a typical connection file like `conn.php`
$conn = new mysqli($host, $user, $password, $db);
// may be few more lines to handle the $conn
if (!function_exists('mysql_escape_string')) {
function mysql_escape_string($sting){ // if mysql_escape_string not available
return $conn->real_escape_string($string); // escape using the $conn instance
}
}
[1]: https://www.php.net/manual/en/mysqli.real-escape-string.php