MySQL and PHP
Copyright 1997-2021 the PHP Documentation Group.
mysql_real_escape_string
Escapes special characters in a string for use in an SQL statement
This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. 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:
mysqli_real_escape_string
|
PDO::quote
|
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 MySQL.
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.
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
had been called with no arguments. If no connection is
found or established, an E_WARNING
level error is generated.
Returns the escaped string, or false
on
error.
Executing this function without a MySQL connection present will
also emit E_WARNING
level PHP errors. Only
execute this function with a valid MySQL connection present.
Example 6.48 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 6.49 mysql_real_escape_string
requires a connection example
This example demonstrates what happens if a MySQL connection is not present when calling this function.
<?php // We have not connected to MySQL $lastname = "O'Reilly"; $_lastname = mysql_real_escape_string($lastname); $query = "SELECT * FROM actors WHERE last_name = '$_lastname'"; var_dump($_lastname); var_dump($query); ?>
The above example will output something similar to:
Warning: mysql_real_escape_string(): No such file or directory in /this/test/script.php on line 5 Warning: mysql_real_escape_string(): A link to the server could not be established in /this/test/script.php on line 5 bool(false) string(41) "SELECT * FROM actors WHERE last_name = ''"
Example 6.50 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.
A MySQL 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 MySQL connection is used.
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.
If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.
mysql_real_escape_string
does not escape
%
and _
. These are wildcards in
MySQL if combined with LIKE
, GRANT
,
or REVOKE
.
mysql_set_charset
|
mysql_client_encoding
|
addslashes
|
stripslashes
|
The magic_quotes_gpc directive |
The magic_quotes_runtime directive |