PHPでのクロスサイトリクエストフォーファリー（CSRF）攻撃を防ぐ方法は？

The most effective way to prevent CSRF attacks in PHP is using anti-CSRF tokens. Generate a secure token via bin2hex(random_bytes(32)), store it in $_SESSION, and include it as a hidden field in forms. Upon submission, verify the token matches the session value; reject mismatches. Regenerate tokens after sensitive actions to prevent replay attacks. Optionally, check $_SERVER['HTTP_REFERER'] to confirm request origin, but don’t rely on it alone. Set SameSite=Strict or Lax for session cookies using session_set_cookie_params(['samesite' => 'Strict']) to limit cross-site cookie transmission. Combining tokens with SameSite cookies provides robust protection. Always implement CSRF tokens for state-changing operations—critical for security.

To prevent Cross-Site Request Forgery (CSRF) attacks in PHP, the most effective method is to use anti-CSRF tokens. These tokens ensure that requests sent to your server originate from your own application and not from a third-party site.

Generate and Use CSRF Tokens

Each time a form is displayed, generate a unique, cryptographically secure token and store it in the user’s session. Include this token as a hidden field in the form. When the form is submitted, verify that the submitted token matches the one stored in the session.

Regenerate Tokens After Use

For higher security, especially after sensitive operations like password changes or payments, regenerate and invalidate old tokens. This prevents token replay attacks.

Validate Request Origins (Optional but Helpful)

Check the HTTP Referer header to ensure the request came from your domain. While not foolproof (the header can be missing or spoofed), it adds an extra layer.

Use SameSite Cookies

Set the SameSite attribute on your session cookies to Strict or Lax. This helps browsers block sending cookies during cross-site requests, reducing CSRF risk.

Combining CSRF tokens with SameSite cookies provides strong protection. Tokens handle form integrity, while SameSite restricts cookie transmission in cross-origin contexts. Basically, always use tokens for state-changing actions—CSRF protection is simple to implement and critical for security.

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