Is SQL Injection a Risk Today

Is SQL injection a risk today?

Quite the contrary. Magic quotes are deprecated in PHP5 and will be completely removed in PHP 5.4, as they brought more confusion to the programming world than they did good. Checking whether magic quotes are active, and escaping any SQL input scrupulously if necessary, is still very, very important... No reason to feel bad though, we've all been there, and my unknowing ass has been saved by magic quotes countless times :)

The PHP manual on magic quotes explains everything.

Should this be considered an SQL injection risk?

Try using ActiveRecord's sanitize_sql_array method: http://api.rubyonrails.org/classes/ActiveRecord/Sanitization/ClassMethods.html#method-i-sanitize_sql_array

Example:

class Job < ActiveRecord::Base
  scope :not_bid_on_by, -> (contractor) do
    joins( sanitize_sql_array [%{
      LEFT JOIN bids ON bids.job_id = jobs.id
      AND bids.contractor_id = ?
    }, contractor.id]).where(bids: { id: nil })
  end
end

SQL - What is the real danger of SQL injection?

SQL injection is not theoretical. There are news reports about real-world data breaches perpetrated using SQL injection practically every month. There's a great site that collects them: https://codecurmudgeon.com/wp/sql-injection-hall-of-shame/

Here's a good one from last month:

https://motherboard.vice.com/en_us/article/vba5nb/fornite-login-hack-epic-games-website

Bugs on Epic Games Site Allowed Hackers to Login to Any ‘Fortnite’ Player’s Account

...

That page, which is now offline, contained two vulnerabilities that are often found in websites: an SQL Injection (or SQLi), and a Cross-Site Scripting (or XSS), according to Check Point researchers.

Regarding the examples you give, I do recommend validating the password in the application code. Then you can differentiate between "no account found" vs. "account found, but password was wrong" (you don't want to reveal this to the user, but you might want to log the error, and possibly lock the account if they have too many failed password attempts).

But regardless, the SQL statement is vulnerable to SQL injection. Not only with the "OR 1=1" trick that you show, but also if you can trick the query into running UNION-based SQL queries:

$query = "SELECT * FROM users WHERE username='' UNION ALL SELECT * FROM INFORMATION_SCHEMA.TABLES -- '";
                                              ^^ $username ...

If the attacker can find an SQL query in your app (not necessarily the search by account name), they can use this technique to query all your tables. Then they can further use UNION techniques to query the data in all the tables, once they know their names.

Regarding your follow-up question:

"How does the data leave the back-end?"

Consider if your password-checking code (for the query above) looks like this:

$query = "SELECT id, username, password_hashed FROM users WHERE username='$username'";

$stmt = $pdo->query($query);
while ($row = $stmt->fetch(PDO::FETCH_NUM)) {
  if (!password_verify($password, $row['password_hashed'])) {
    die("Invalid login for user {$row['username']}");
  }
}

See? The result from the SQL query is output to the user. To the developer of this code, it seems obvious that since they just queried for $username then that's the value that would be returned by the query. They feel that $row['username'] is safe to use.

But it's not — it's some data from the other part of the UNION. By using CONCAT() and GROUP_CONCAT(), the attacker can even put together multiple columns from multiple rows. And they do. It may take them several tries to get their attack query to have the right number of columns in the right positions, but they apparently have nothing better to do.

Is there any injection risk if no user input was sent to database?

You are right. Your SQL statement includes no parameters outside of itself, so there is no vector for injection. While injection attacks ARE possible on SELECT statements, in your case the query is not created dynamically so cannot be tampered with.

Are Parameters really enough to prevent Sql injections?

Placeholders are enough to prevent injections. You might still be open to buffer overflows, but that is a completely different flavor of attack from an SQL injection (the attack vector would not be SQL syntax but binary). Since the parameters passed will all be escaped properly, there isn't any way for an attacker to pass data that will be treated like "live" SQL.

You can't use functions inside placeholders, and you can't use placeholders as column or table names, because they are escaped and quoted as string literals.

However, if you use parameters as part of a string concatenation inside your dynamic query, you are still vulnerable to injection, because your strings will not be escaped but will be literal. Using other types for parameters (such as integer) is safe.

That said, if you're using use input to set the value of something like security_level, then someone could just make themselves administrators in your system and have a free-for-all. But that's just basic input validation, and has nothing to do with SQL injection.

How can prepared statements protect from SQL injection attacks?

The idea is very simple - the query and the data are sent to the database server separately.

That's all.

The root of the SQL injection problem is in the mixing of the code and the data.

In fact, our SQL query is a legitimate program.
And we are creating such a program dynamically, adding some data on the fly. Thus, the data may interfere with the program code and even alter it, as every SQL injection example shows it (all examples in PHP/Mysql):

$expected_data = 1;
$query = "SELECT * FROM users where id=$expected_data";

will produce a regular query

SELECT * FROM users where id=1

while this code

$spoiled_data = "1; DROP TABLE users;"
$query        = "SELECT * FROM users where id=$spoiled_data";

will produce a malicious sequence

SELECT * FROM users where id=1; DROP TABLE users;

It works because we are adding the data directly to the program body and it becomes a part of the program, so the data may alter the program, and depending on the data passed, we will either have a regular output or a table users deleted.

While in case of prepared statements we don't alter our program, it remains intact
That's the point.

We are sending a program to the server first

$db->prepare("SELECT * FROM users where id=?");

where the data is substituted by some variable called a parameter or a placeholder.

Note that exactly the same query is sent to the server, without any data in it! And then we're sending the data with the second request, essentially separated from the query itself:

$db->execute($data);

so it can't alter our program and do any harm.

Quite simple - isn't it?

The only thing I have to add that always omitted in the every manual:

Prepared statements can protect only data literals, but cannot be used with any other query part.

So, once we have to add, say, a dynamical identifier - a field name, for example - prepared statements can't help us. I've explained the matter recently, so I won't repeat myself.

Is string_split() injection safe?

There is no outright injection issue in the sense that arbitrary code cannot be executed. This is because, ultimately, @commaSeparatedListOfValues remains a string, and is never parsed into actual code.

The only injection issue is if you are explicitly passing say three value, and one of them contained a comma.

For example, if you had a web page accepting a list of items, and the user entered first sec,ond third. If you mash these together with , then your SQL code will end up interpreting this as four separate values first sec ond third.

For this and other performance and correctness reasons, it's probably better to just use a Table Valued Parameter.

How can I prevent SQL injection in PHP?

The correct way to avoid SQL injection attacks, no matter which database you use, is to separate the data from SQL, so that data stays data and will never be interpreted as commands by the SQL parser. It is possible to create an SQL statement with correctly formatted data parts, but if you don't fully understand the details, you should always use prepared statements and parameterized queries. These are SQL statements that are sent to and parsed by the database server separately from any parameters. This way it is impossible for an attacker to inject malicious SQL.

You basically have two options to achieve this:

Using PDO (for any supported database driver):

$stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
$stmt->execute([ 'name' => $name ]);

foreach ($stmt as $row) {
    // Do something with $row
}

Using MySQLi (for MySQL):

Since PHP 8.2+ we can make use of execute_query() which prepares, binds parameters, and executes SQL statement in one method:

$result = $dbConnection->execute_query('SELECT * FROM employees WHERE name = ?', [$name]);

while ($row = $result->fetch_assoc()) {
    // Do something with $row
}

Up to PHP8.1:

$stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?');
$stmt->bind_param('s', $name); // 's' specifies the variable type => 'string'
$stmt->execute();

$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
    // Do something with $row
}

If you're connecting to a database other than MySQL, there is a driver-specific second option that you can refer to (for example, pg_prepare() and pg_execute() for PostgreSQL). PDO is the universal option.

Correctly setting up the connection

PDO

Note that when using PDO to access a MySQL database real prepared statements are not used by default. To fix this you have to disable the emulation of prepared statements. An example of creating a connection using PDO is:

$dbConnection = new PDO('mysql:dbname=dbtest;host=127.0.0.1;charset=utf8mb4', 'user', 'password');

$dbConnection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

In the above example, the error mode isn't strictly necessary, but it is advised to add it. This way PDO will inform you of all MySQL errors by means of throwing the PDOException.

What is mandatory, however, is the first setAttribute() line, which tells PDO to disable emulated prepared statements and use real prepared statements. This makes sure the statement and the values aren't parsed by PHP before sending it to the MySQL server (giving a possible attacker no chance to inject malicious SQL).

Although you can set the charset in the options of the constructor, it's important to note that 'older' versions of PHP (before 5.3.6) silently ignored the charset parameter in the DSN.

Mysqli

For mysqli we have to follow the same routine:

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); // error reporting
$dbConnection = new mysqli('127.0.0.1', 'username', 'password', 'test');
$dbConnection->set_charset('utf8mb4'); // charset

Explanation

The SQL statement you pass to prepare is parsed and compiled by the database server. By specifying parameters (either a ? or a named parameter like :name in the example above) you tell the database engine where you want to filter on. Then when you call execute, the prepared statement is combined with the parameter values you specify.

The important thing here is that the parameter values are combined with the compiled statement, not an SQL string. SQL injection works by tricking the script into including malicious strings when it creates SQL to send to the database. So by sending the actual SQL separately from the parameters, you limit the risk of ending up with something you didn't intend.

Any parameters you send when using a prepared statement will just be treated as strings (although the database engine may do some optimization so parameters may end up as numbers too, of course). In the example above, if the $name variable contains 'Sarah'; DELETE FROM employees the result would simply be a search for the string "'Sarah'; DELETE FROM employees", and you will not end up with an empty table.

Another benefit of using prepared statements is that if you execute the same statement many times in the same session it will only be parsed and compiled once, giving you some speed gains.

Oh, and since you asked about how to do it for an insert, here's an example (using PDO):

$preparedStatement = $db->prepare('INSERT INTO table (column) VALUES (:column)');

$preparedStatement->execute([ 'column' => $unsafeValue ]);

Can prepared statements be used for dynamic queries?

While you can still use prepared statements for the query parameters, the structure of the dynamic query itself cannot be parametrized and certain query features cannot be parametrized.

For these specific scenarios, the best thing to do is use a whitelist filter that restricts the possible values.

// Value whitelist
// $dir can only be 'DESC', otherwise it will be 'ASC'
if (empty($dir) || $dir !== 'DESC') {
   $dir = 'ASC';
}

Is SQL Injection a Risk Today