Dynamically building SQL query strings can result in broken SQL syntax and open SQL injection attacks.

Why is this an issue?

When SQL queries are constructed by concatenating or formatting user-supplied values directly into the query string, the structure of the query itself can be altered by a malicious input. This rule flags calls to SQL execution functions where the query string is built using string concatenation or format operators rather than parameterized queries or prepared statements. Unlike rule {rule:php:S3649}, this rule does not perform taint analysis — it flags all dynamically formatted SQL queries as a potential risk regardless of the data source.

What is the potential impact?

SQL injection

If any part of a dynamically formatted query string originates from untrusted input, an attacker can manipulate the query to read, modify, or delete data they should not have access to, bypass authentication checks, or in some configurations execute operating system commands.

How to fix it

Code examples

The following code builds a SQL query by concatenating a value directly into the query string.

Noncompliant code example

$id = $_GET['id'];
mysql_connect('localhost', $username, $password) or die('Could not connect: ' . mysql_error());
mysql_select_db('myDatabase') or die('Could not select database');

$result = mysql_query("SELECT * FROM myTable WHERE id = " . $id);  // Noncompliant, could be susceptible to SQL injection

while ($row = mysql_fetch_object($result)) {
    echo $row->name;
}

Compliant solution

$id = $_GET['id'];
try {
    $conn = new PDO('mysql:host=localhost;dbname=myDatabase', $username, $password);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $stmt = $conn->prepare('SELECT * FROM myTable WHERE id = :id');
    $stmt->execute(array('id' => $id));

    while($row = $stmt->fetch(PDO::FETCH_OBJ)) {
        echo $row->name;
    }
} catch(PDOException $e) {
    echo 'ERROR: ' . $e->getMessage();
}

Exceptions

No issue will be raised if one of the functions is called with a hard-coded string (no concatenation) and this string does not contain a $ sign.

$result = mysql_query("SELECT * FROM myTable WHERE id = 42") or die('Query failed: ' . mysql_error());  // Compliant

The current implementation does not follow variables. It will only detect SQL queries which are concatenated or contain a $ sign directly in the function call.

$query = "SELECT * FROM myTable WHERE id = " . $id;
$result = mysql_query($query);  // Not detected by this rule

Resources

Articles & blog posts

Standards