All SQL Injection is due to dynamic SQL queries. Strongly consider prohibiting dynamic SQL queries completely.

Injection flaws occur when an application sends untrusted data to an interpreter. Injection flaws are very prevalent, particularly in legacy code. They are often found in SQL, LDAP, Xpath, or NoSQL queries; OS commands; XML parsers, SMTP Headers, program arguments, etc. Injection flaws are easy to discover when examining code, but frequently hard to discover via testing. Scanners and fuzzers can help attackers find injection flaws.

Example attacks

Primary Defenses

Scenario #1: The application uses untrusted data in the construction of the following vulnerable SQL call:

String query = "SELECT * FROM accounts WHERE custID='" + request.getParameter("id") + "'";

Scenario #2: Similarly, an application’s blind trust in frameworks may result in queries that are still vulnerable, (e.g., Hibernate Query Language (HQL)):

Query HQLQuery = SESSION.createQuery(“FROM accounts WHERE custID='“ + request.getParameter("id") + "'");

In both cases, the attacker modifies the ‘id’ parameter value in her browser to send: ' or '1'='1.

For example: http://example.com/app/accountView?id=' or '1'='1

This changes the meaning of both queries to return all the records from the accounts table. More dangerous attacks could modify data or even invoke stored procedures.

Scenario #3: Code to do an insert into the database could also be vulnerable.

$sql = "INSERT INTO Students (Name) VALUES ('" . $studentName . "');";
execute_sql($sql);

The first line creates a string containing an SQL INSERT statement. The content of the $studentName variable is glued into the SQL statement. The second line sends the resulting SQL statement to the database. The pitfall of this code is that outside data, in this case the content of $studentName, becomes part of the SQL statement.

First let's see what the SQL statement looks like if we insert a student named John:

INSERT INTO Students (Name) VALUES ('John');

This does exactly what we want: it inserts John into the Students table.

Now we insert some injection code by setting $studentName to Robert'); DROP TABLE Students;--. The SQL statement becomes:

INSERT INTO Students (Name) VALUES ('Robert'); DROP TABLE Students;--');

This inserts Robert into the Students table. However, the INSERT statement is now followed by a DROP TABLE statement which removes the entire Students table. Ouch!

• 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) );

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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