drupal-security

Drupal Security

Critical Security Patterns

SQL Injection Prevention

NEVER concatenate user input into queries:

// VULNERABLE - SQL injection
$query = "SELECT * FROM users WHERE name = '" . $name . "'";
$result = $connection->query($query);

// SAFE - parameterized query
$result = $connection->select('users', 'u')
  ->fields('u')
  ->condition('name', $name)
  ->execute();

// SAFE - placeholder
$result = $connection->query(
  'SELECT * FROM {users} WHERE name = :name',
  [':name' => $name]
);

XSS Prevention

Always escape output. Trust the render system:

// VULNERABLE - raw HTML output
return ['#markup' => $user_input];
return ['#markup' => '<div>' . $title . '</div>'];

// SAFE - plain text (auto-escaped)
return ['#plain_text' => $user_input];

// SAFE - use proper render elements
return [
  '#type' => 'html_tag',
  '#tag' => 'div',
  '#value' => $title,  // Escaped automatically
];

// SAFE - Twig auto-escapes
{{ variable }}  // Escaped
{{ variable|raw }}  // DANGEROUS - only for trusted HTML

For admin-only content:

use Drupal\Component\Utility\Xss;

// Filter but allow safe HTML tags
$safe = Xss::filterAdmin($user_html);

Note: Never pass untrusted user input into #markup. Prefer #plain_text, Twig auto-escaping, or safe render elements.

Access Control

Always verify permissions:

// In routing.yml
my_module.admin:
  path: '/admin/my-module'
  requirements:
    _permission: 'administer my_module'  # Required!

// In code
if (!$this->currentUser->hasPermission('administer my_module')) {
  throw new AccessDeniedHttpException();
}

// Entity queries - check access!
$query = $this->entityTypeManager
  ->getStorage('node')
  ->getQuery()
  ->accessCheck(TRUE)  // CRITICAL - never FALSE unless intentional
  ->condition('type', 'article');

CSRF Protection

Forms automatically include CSRF tokens. For custom AJAX:

// Include token in AJAX requests
$build['#attached']['drupalSettings']['myModule']['token'] =
  \Drupal::csrfToken()->get('my_module_action');

Note: Prefer dependency injection over direct \Drupal::service() or \Drupal:: calls in classes.

// Validate in controller
if (!$this->csrfToken->validate($token, 'my_module_action')) {
  throw new AccessDeniedHttpException('Invalid token');
}

File Upload Security

$validators = [
  'file_validate_extensions' => ['pdf doc docx'],  // Whitelist extensions
  'file_validate_size' => [25600000],  // 25MB limit
  'FileSecurity' => [],  // Drupal 10.2+ - blocks dangerous files
];

// NEVER trust file extension alone - check MIME type
$file_mime = $file->getMimeType();
$allowed_mimes = ['application/pdf', 'application/msword'];
if (!in_array($file_mime, $allowed_mimes)) {
  // Reject file
}

Sensitive Data

// NEVER log sensitive data
$this->logger->info('User @user logged in', ['@user' => $username]);
// NOT: $this->logger->info('Login: ' . $username . ':' . $password);

// NEVER expose in error messages
throw new \Exception('Database error');  // Generic
// NOT: throw new \Exception('Query failed: ' . $query);

// Use environment variables for secrets
$api_key = getenv('MY_API_KEY');
// NOT: $api_key = 'hardcoded-secret-key';

Red Flags to Watch For

When you see these patterns, immediately warn:

Pattern	Risk	Fix
String concatenation in SQL	SQL injection	Use query builder
#markup with variables	XSS	Use #plain_text
accessCheck(FALSE)	Access bypass	Use accessCheck(TRUE)
Missing _permission in routes	Unauthorized access	Add permission
Custom controller with no access check	Unauthorized access	Add route permission or access callback
{{ var|raw }} in Twig	XSS	Remove |raw
Hardcoded passwords/keys	Credential exposure	Use env vars
eval() or exec()	Code injection	Avoid entirely
unserialize() on user data	Object injection	Use JSON
Missing CSRF validation in custom endpoints	CSRF attack	Validate token using csrf_token service
File upload without validation	Malicious file upload	Validate extension, size, and MIME type
Direct \Drupal:: usage in classes	Hard to test / bad practice	Use dependency injection
Logging sensitive data	Information disclosure	Mask or avoid logging sensitive fields