`mysql_real_escape_string`

mysql_real_escape_string
Escapes special characters in a string for use in an SQL statement

Description

string mysql_real_escape_string(string 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 MariaDB.

Parameters

unescaped_string: The string that is to be escaped.
link_identifier: The MariaDB 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_WARNING level error is generated.

Return Values

Returns the escaped string, or FALSE on error.

Examples

Example 20.62. 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 20.63. 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 MariaDB 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 MariaDB connection is required before using mysql_real_escape_string otherwise an error of level E_WARNING is generated, and FALSE is returned. If link_identifier isn't defined, the last MariaDB 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 MariaDB if combined with LIKE, GRANT, or REVOKE.