• Use Prepared Statements (Parameterized Queries)
• Use Stored Procedures
• Escape all User Supplied Input

The use of prepared statements with variable binding (aka parameterized queries) is how all developers should first be taught how to write database queries. Parameterized queries force the developer to first define all the SQL code, and then pass in each parameter to the query later. This coding style allows the database to distinguish between code and data, regardless of what user input is supplied.

Prepared statements ensure that an attacker is not able to change the intent of a query, even if SQL commands are inserted by an attacker. In the safe example below, if an attacker were to enter the userID of tom' or '1'='1, the parameterized query would not be vulnerable and would instead look for a username which literally matched the entire string tom' or '1'='1.

The MySQL Improved extension handles bound parameters.

$stmt = $db->prepare('update people set name = ? where id = ?');
$stmt->bind_param('si',$name,$id);
$stmt->execute();

ADODB provides a way to prepare, bind and execute all in the same method call.

$dbConnection = NewADOConnection($connectionString);
$sqlResult = $dbConnection->Execute(
    'SELECT user_id,first_name,last_name FROM users WHERE username=? AND password=?',
    array($_REQUEST['username'], sha1($_REQUEST['password'])
);

$stmt = odbc_prepare( $conn, 'SELECT * FROM users WHERE email = ?' );
$success = odbc_execute( $stmt, array($email) );

or:

$res = odbc_exec($conn, 'SELECT * FROM users WHERE email = ?', array($email));
$sth = $dbh->prepare('SELECT * FROM users WHERE email = :email');
$sth->execute(array(':email' => $email));

Here's the long way to do bind parameters.

$dbh = new PDO('mysql:dbname=testdb;host=127.0.0.1', $user, $password);
$stmt = $dbh->prepare('INSERT INTO REGISTRY (name, value) VALUES (:name, :value)');
$stmt->bindParam(':name', $name);
$stmt->bindParam(':value', $value);
 
// insert one row
$name = 'one';
$value = 1;
$stmt->execute();

And a shorter way to pass things in.

$dbh = new PDO('mysql:dbname=testdb;host=127.0.0.1', $user, $password);
$stmt = $dbh->prepare('UPDATE people SET name = :new_name WHERE id = :id');
$stmt->execute( array('new_name' => $name, 'id' => $id) );

$result = pg_query_params( $dbh, 'SELECT * FROM users WHERE email = $1', array($email) );

TODO : Check if this works?

It seems to me that it's sufficient to escape single quotes with single quotes, ie. '' (2 single quotes) instead of \'.

For example,

$mysql['username'] = str_replace(array('\\', '\''), array('\\\\', '\\\''), $_POST['username']);
 
$mysql['password'] = str_replace(array('\\', '\''), array('\\\\', '\\\''), $_POST['password']);

will make the injection attempt successful, whereas

$mysql['username'] = str_replace(array('\\', '\''), array('\\\\', '\'\''), $_POST['username']);
 
$mysql['password'] = str_replace(array('\\', '\''), array('\\\\', '\'\''), $_POST['password']);

will make the injection attempt fail.

Isn't the latter method (str_replace(array('\\', '\), array('\\\\', '\'\), $data)) always sufficient for preparing data for a mysql query where apostrophe is the enclosure character? If so, is there any reason why we should still rather be using mysql_real_escape_string()?

The JDBC API has a class called PreparedStatement which allows the programmer to safely insert user-supplied data into a SQL query. The location of each input value in the query string is marked with a question mark. The various set*() methods are then used to safely perform the insertion.

String name = //user input
int age = //user input
Connection connection = DriverManager.getConnection(...);
PreparedStatement statement = connection.prepareStatement(
        "SELECT * FROM people WHERE lastName = ? AND age > ?" );
statement.setString(1, name); //lastName is a VARCHAR
statement.setInt(2, age); //age is an INT
ResultSet rs = statement.executeQuery();
while (rs.next()){
    //...
}

Hibernate uses named parameters to safely insert data into a query. A named parameter consists of a colon, followed by a unique name for the parameter.

String name = //user input
int age = //user input
Session session = //...
Query query = session.createQuery("from People where lastName = :name and age > :age");
query.setString("name", name);
query.setInteger("age", age);
Iterator people = query.iterate();

Perl's DBI, available on the CPAN, supports parameterized SQL calls. Both the do method and prepare method support parameters (“placeholders”, as they call them) for most database drivers. For example:

$sth = $dbh->prepare("SELECT * FROM users WHERE email = ?");
foreach my $email (@emails) {
    $sth->execute($email);
    $row = $sth->fetchrow_hashref;
    [...]
}

However, you can't use parameterization for identifiers (table names, column names) so you need to use DBI's quote_identifier() method for that:

# Make sure a table name we want to use is safe:
my $quoted_table_name = $dbh->quote_identifier($table_name);
 
# Assume @cols contains a list of column names you need to fetch:
my $cols = join ',', map { $dbh->quote_identifier($_) } @cols;
 
my $sth = $dbh->prepare("SELECT $cols FROM $quoted_table_name ...");

You could also avoid writing SQL by hand by using DBIx::Class, SQL::Abstract etc to generate your SQL for you programmatically.

Use sqlite3_prepare() to create a statement object.

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