Can Prepared Statements Handle Parameterized Table Names to Prevent SQL Injection?

Prepared Statements: Can They Handle Parameterized Table Names?

This article addresses the crucial question of whether prepared statements can effectively handle parameterized table names to prevent SQL injection vulnerabilities.

The Problem:

Directly embedding user-supplied data into SQL queries, including table names, is a major security risk. Consider this example:

function insertRow( $db, $mysqli, $new_table, $Partner, $Merchant, $ips, $score, $category, $overall, $protocol )
{
    $statement = $mysqli->prepare("INSERT INTO " .$new_table . " VALUES (?,?,?,?,?,?,?);");
    mysqli_stmt_bind_param( $statment, 'sssisss', $Partner, $Merchant, $ips, $score, $category, $overall, $protocol );
    $statement->execute();
}

The concatenation .$new_table. makes this function vulnerable to SQL injection if $new_table is not properly sanitized.

Attempting Parameterization:

A common attempt to mitigate this is to try parameterizing the table name:

function insertRow( $db, $mysqli, $new_table, $Partner, $Merchant, $ips, $score, $category, $overall, $protocol )
{
    $statement = $mysqli->prepare("INSERT INTO (?) VALUES (?,?,?,?,?,?,?);");
    mysqli_stmt_bind_param( $statment, 'ssssisss', $new_table, $Partner, $Merchant, $ips, $score, $category, $overall, $protocol );
    $statement->execute();
}

The Reality:

Unfortunately, this approach fails. Prepared statements are designed to protect against runtime value injection, not against altering the structure of the SQL query itself. The database parser interprets the table name as part of the query's structure, not as a runtime parameter. Replacing it with a placeholder results in invalid SQL.

Even with systems offering prepared statement emulation, like PDO, the result would be an invalid query (e.g., SELECT * FROM 'mytable' instead of SELECT * FROM mytable).

The Solution:

The only reliable way to prevent SQL injection when dealing with user-supplied table names is to employ a strict whitelist. This involves pre-defining a list of allowed table names and ensuring that any user-provided table name is checked against this whitelist before it's used in a query. Never directly use user input to construct SQL queries involving table names.

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