Key ways to prevent SQL injection in PHP include: 1. Use preprocessing statements (such as PDO or MySQLi) to separate SQL code and data; 2. Turn off simulated preprocessing mode to ensure true preprocessing; 3. Filter and verify user input, such as using is_numeric() and filter_var(); 4. Avoid directly splicing SQL strings and use parameter binding instead; 5. Turn off error display in the production environment and record error logs. These measures comprehensively prevent SQL injection risks in terms of mechanisms and details.
The key to preventing SQL injection in PHP is to handle user input correctly and use a secure database operation method . Don’t think that filtering a few keywords can be done. Real and effective protection needs to start from the source and mechanism.
Use Prepared Statements
This is the most recommended method at present. Preprocessing statements can separate SQL code from data, fundamentally preventing injection.
- If you are using MySQL, it is recommended to use PDO or MySQLi , both of which support preprocessing.
- Example (taking PDO as an example):
$stmt = $pdo->prepare('SELECT * FROM users WHERE email = ?'); $stmt->execute([$email]); $user = $stmt->fetch();
In this way, even if $email is malicious input, it will be processed as a normal string and will not affect the SQL structure.
Note: Be sure to turn off the "Simulation Preprocessing" mode to ensure that preprocessing is actually used:
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
Filter and verify user input
Although preprocessing is already very powerful, it is still necessary to conduct basic checks on user input.
- For fields of numeric types, use
is_numeric()or cast; - For formats such as mailbox, URL, etc., you can use
filter_var()function; - For example, verify the email:
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) { // The email address is illegal, refuse to process}
This not only prevents injection, but also improves program robustness and reduces invalid requests.
Avoid splicing of SQL strings
A common mistake for beginners is to splice variables directly into SQL, such as:
$sql = "SELECT * FROM users WHERE id = " . $_GET['id'];
This writing method is extremely risky. Even if you do filtering, it will be difficult to cover all situations. Parameter binding should always be used instead of string stitching.
Do not expose error messages to the front end
During development, we like to turn on error prompts for easy debugging, but we must turn it off in production environment:
ini_set('display_errors', 0);
Otherwise, the attacker can understand your database structure by reporting an error message, thereby conducting more accurate attacks.
It is also recommended to log error logs instead of outputting them directly:
error_reporting(E_ALL); ini_set('log_errors', 1); ini_set('error_log', '/path/to/error.log');
Basically that's it. SQL injection is not a profound attack method, but many vulnerabilities are caused by neglecting details. As long as you develop good habits in development, you can effectively avoid such problems.
The above is the detailed content of How to prevent SQL injection in PHP. For more information, please follow other related articles on the PHP Chinese website!
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