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CsrfProtectionMiddleware.php
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CsrfProtectionMiddleware.php
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<?php
declare(strict_types=1);
/**
* CakePHP(tm) : Rapid Development Framework (https://cakephp.org)
* Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
*
* Licensed under The MIT License
* For full copyright and license information, please see the LICENSE.txt
* Redistributions of files must retain the above copyright notice.
*
* @copyright Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
* @link https://cakephp.org CakePHP(tm) Project
* @since 3.5.0
* @license https://www.opensource.org/licenses/mit-license.php MIT License
*/
namespace Cake\Http\Middleware;
use ArrayAccess;
use Cake\Http\Cookie\Cookie;
use Cake\Http\Cookie\CookieInterface;
use Cake\Http\Exception\InvalidCsrfTokenException;
use Cake\Http\Response;
use Cake\Utility\Hash;
use Cake\Utility\Security;
use InvalidArgumentException;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\MiddlewareInterface;
use Psr\Http\Server\RequestHandlerInterface;
use RuntimeException;
use function Cake\Core\deprecationWarning;
use function Cake\I18n\__d;
/**
* Provides CSRF protection & validation.
*
* This middleware adds a CSRF token to a cookie. The cookie value is compared to
* token in request data, or the X-CSRF-Token header on each PATCH, POST,
* PUT, or DELETE request. This is known as "double submit cookie" technique.
*
* If the request data is missing or does not match the cookie data,
* an InvalidCsrfTokenException will be raised.
*
* This middleware integrates with the FormHelper automatically and when
* used together your forms will have CSRF tokens automatically added
* when `$this->Form->create(...)` is used in a view.
*
* @see https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html#double-submit-cookie
*/
class CsrfProtectionMiddleware implements MiddlewareInterface
{
/**
* Config for the CSRF handling.
*
* - `cookieName` The name of the cookie to send.
* - `expiry` A strotime compatible value of how long the CSRF token should last.
* Defaults to browser session.
* - `secure` Whether the cookie will be set with the Secure flag. Defaults to false.
* - `httponly` Whether the cookie will be set with the HttpOnly flag. Defaults to false.
* - `samesite` "SameSite" attribute for cookies. Defaults to `null`.
* Valid values: `CookieInterface::SAMESITE_LAX`, `CookieInterface::SAMESITE_STRICT`,
* `CookieInterface::SAMESITE_NONE` or `null`.
* - `field` The form field to check. Changing this will also require configuring
* FormHelper.
*
* @var array<string, mixed>
*/
protected $_config = [
'cookieName' => 'csrfToken',
'expiry' => 0,
'secure' => false,
'httponly' => false,
'samesite' => null,
'field' => '_csrfToken',
];
/**
* Callback for deciding whether to skip the token check for particular request.
*
* CSRF protection token check will be skipped if the callback returns `true`.
*
* @var callable|null
*/
protected $skipCheckCallback;
/**
* @var int
*/
public const TOKEN_VALUE_LENGTH = 16;
/**
* Tokens have an hmac generated so we can ensure
* that tokens were generated by our application.
*
* Should be TOKEN_VALUE_LENGTH + strlen(hmac)
*
* We are currently using sha1 for the hmac which
* creates 40 bytes.
*
* @var int
*/
public const TOKEN_WITH_CHECKSUM_LENGTH = 56;
/**
* Constructor
*
* @param array<string, mixed> $config Config options. See $_config for valid keys.
*/
public function __construct(array $config = [])
{
if (array_key_exists('httpOnly', $config)) {
$config['httponly'] = $config['httpOnly'];
deprecationWarning('Option `httpOnly` is deprecated. Use lowercased `httponly` instead.');
}
$this->_config = $config + $this->_config;
}
/**
* Checks and sets the CSRF token depending on the HTTP verb.
*
* @param \Psr\Http\Message\ServerRequestInterface $request The request.
* @param \Psr\Http\Server\RequestHandlerInterface $handler The request handler.
* @return \Psr\Http\Message\ResponseInterface A response.
*/
public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
{
$method = $request->getMethod();
$hasData = in_array($method, ['PUT', 'POST', 'DELETE', 'PATCH'], true)
|| $request->getParsedBody();
if (
$hasData
&& $this->skipCheckCallback !== null
&& call_user_func($this->skipCheckCallback, $request) === true
) {
$request = $this->_unsetTokenField($request);
return $handler->handle($request);
}
if ($request->getAttribute('csrfToken')) {
throw new RuntimeException(
'A CSRF token is already set in the request.' .
"\n" .
'Ensure you do not have the CSRF middleware applied more than once. ' .
'Check both your `Application::middleware()` method and `config/routes.php`.'
);
}
$cookies = $request->getCookieParams();
$cookieData = Hash::get($cookies, $this->_config['cookieName']);
if (is_string($cookieData) && $cookieData !== '') {
try {
$request = $request->withAttribute('csrfToken', $this->saltToken($cookieData));
} catch (InvalidArgumentException $e) {
$cookieData = null;
}
}
if ($method === 'GET' && $cookieData === null) {
$token = $this->createToken();
$request = $request->withAttribute('csrfToken', $this->saltToken($token));
/** @var mixed $response */
$response = $handler->handle($request);
return $this->_addTokenCookie($token, $request, $response);
}
if ($hasData) {
$this->_validateToken($request);
$request = $this->_unsetTokenField($request);
}
return $handler->handle($request);
}
/**
* Set callback for allowing to skip token check for particular request.
*
* The callback will receive request instance as argument and must return
* `true` if you want to skip token check for the current request.
*
* @deprecated 4.1.0 Use skipCheckCallback instead.
* @param callable $callback A callable.
* @return $this
*/
public function whitelistCallback(callable $callback)
{
deprecationWarning('`whitelistCallback()` is deprecated. Use `skipCheckCallback()` instead.');
$this->skipCheckCallback = $callback;
return $this;
}
/**
* Set callback for allowing to skip token check for particular request.
*
* The callback will receive request instance as argument and must return
* `true` if you want to skip token check for the current request.
*
* @param callable $callback A callable.
* @return $this
*/
public function skipCheckCallback(callable $callback)
{
$this->skipCheckCallback = $callback;
return $this;
}
/**
* Remove CSRF protection token from request data.
*
* @param \Psr\Http\Message\ServerRequestInterface $request The request object.
* @return \Psr\Http\Message\ServerRequestInterface
*/
protected function _unsetTokenField(ServerRequestInterface $request): ServerRequestInterface
{
$body = $request->getParsedBody();
if (is_array($body)) {
unset($body[$this->_config['field']]);
$request = $request->withParsedBody($body);
}
return $request;
}
/**
* Create a new token to be used for CSRF protection
*
* @return string
* @deprecated 4.0.6 Use {@link createToken()} instead.
*/
protected function _createToken(): string
{
deprecationWarning('_createToken() is deprecated. Use createToken() instead.');
return $this->createToken();
}
/**
* Test if the token predates salted tokens.
*
* These tokens are hexadecimal values and equal
* to the token with checksum length. While they are vulnerable
* to BREACH they should rotate over time and support will be dropped
* in 5.x.
*
* @param string $token The token to test.
* @return bool
*/
protected function isHexadecimalToken(string $token): bool
{
return preg_match('/^[a-f0-9]{' . static::TOKEN_WITH_CHECKSUM_LENGTH . '}$/', $token) === 1;
}
/**
* Create a new token to be used for CSRF protection
*
* @return string
*/
public function createToken(): string
{
$value = Security::randomBytes(static::TOKEN_VALUE_LENGTH);
return base64_encode($value . hash_hmac('sha1', $value, Security::getSalt()));
}
/**
* Apply entropy to a CSRF token
*
* To avoid BREACH apply a random salt value to a token
* When the token is compared to the session the token needs
* to be unsalted.
*
* @param string $token The token to salt.
* @return string The salted token with the salt appended.
*/
public function saltToken(string $token): string
{
if ($this->isHexadecimalToken($token)) {
return $token;
}
$decoded = base64_decode($token, true);
if ($decoded === false) {
throw new InvalidArgumentException('Invalid token data.');
}
$length = strlen($decoded);
$salt = Security::randomBytes($length);
$salted = '';
for ($i = 0; $i < $length; $i++) {
// XOR the token and salt together so that we can reverse it later.
$salted .= chr(ord($decoded[$i]) ^ ord($salt[$i]));
}
return base64_encode($salted . $salt);
}
/**
* Remove the salt from a CSRF token.
*
* If the token is not TOKEN_VALUE_LENGTH * 2 it is an old
* unsalted value that is supported for backwards compatibility.
*
* @param string $token The token that could be salty.
* @return string An unsalted token.
*/
public function unsaltToken(string $token): string
{
if ($this->isHexadecimalToken($token)) {
return $token;
}
$decoded = base64_decode($token, true);
if ($decoded === false || strlen($decoded) !== static::TOKEN_WITH_CHECKSUM_LENGTH * 2) {
return $token;
}
$salted = substr($decoded, 0, static::TOKEN_WITH_CHECKSUM_LENGTH);
$salt = substr($decoded, static::TOKEN_WITH_CHECKSUM_LENGTH);
$unsalted = '';
for ($i = 0; $i < static::TOKEN_WITH_CHECKSUM_LENGTH; $i++) {
// Reverse the XOR to desalt.
$unsalted .= chr(ord($salted[$i]) ^ ord($salt[$i]));
}
return base64_encode($unsalted);
}
/**
* Verify that CSRF token was originally generated by the receiving application.
*
* @param string $token The CSRF token.
* @return bool
*/
protected function _verifyToken(string $token): bool
{
// If we have a hexadecimal value we're in a compatibility mode from before
// tokens were salted on each request.
if ($this->isHexadecimalToken($token)) {
$decoded = $token;
} else {
$decoded = base64_decode($token, true);
}
if (!$decoded || strlen($decoded) <= static::TOKEN_VALUE_LENGTH) {
return false;
}
$key = substr($decoded, 0, static::TOKEN_VALUE_LENGTH);
$hmac = substr($decoded, static::TOKEN_VALUE_LENGTH);
$expectedHmac = hash_hmac('sha1', $key, Security::getSalt());
return hash_equals($hmac, $expectedHmac);
}
/**
* Add a CSRF token to the response cookies.
*
* @param string $token The token to add.
* @param \Psr\Http\Message\ServerRequestInterface $request The request to validate against.
* @param \Psr\Http\Message\ResponseInterface $response The response.
* @return \Psr\Http\Message\ResponseInterface $response Modified response.
*/
protected function _addTokenCookie(
string $token,
ServerRequestInterface $request,
ResponseInterface $response
): ResponseInterface {
$cookie = $this->_createCookie($token, $request);
if ($response instanceof Response) {
return $response->withCookie($cookie);
}
return $response->withAddedHeader('Set-Cookie', $cookie->toHeaderValue());
}
/**
* Validate the request data against the cookie token.
*
* @param \Psr\Http\Message\ServerRequestInterface $request The request to validate against.
* @return void
* @throws \Cake\Http\Exception\InvalidCsrfTokenException When the CSRF token is invalid or missing.
*/
protected function _validateToken(ServerRequestInterface $request): void
{
$cookie = Hash::get($request->getCookieParams(), $this->_config['cookieName']);
if (!$cookie || !is_string($cookie)) {
throw new InvalidCsrfTokenException(__d('cake', 'Missing or incorrect CSRF cookie type.'));
}
if (!$this->_verifyToken($cookie)) {
$exception = new InvalidCsrfTokenException(__d('cake', 'Missing or invalid CSRF cookie.'));
$expiredCookie = $this->_createCookie('', $request)->withExpired();
$exception->setHeader('Set-Cookie', $expiredCookie->toHeaderValue());
throw $exception;
}
$body = $request->getParsedBody();
if (is_array($body) || $body instanceof ArrayAccess) {
$post = (string)Hash::get($body, $this->_config['field']);
$post = $this->unsaltToken($post);
if (hash_equals($post, $cookie)) {
return;
}
}
$header = $request->getHeaderLine('X-CSRF-Token');
$header = $this->unsaltToken($header);
if (hash_equals($header, $cookie)) {
return;
}
throw new InvalidCsrfTokenException(__d(
'cake',
'CSRF token from either the request body or request headers did not match or is missing.'
));
}
/**
* Create response cookie
*
* @param string $value Cookie value
* @param \Psr\Http\Message\ServerRequestInterface $request The request object.
* @return \Cake\Http\Cookie\CookieInterface
*/
protected function _createCookie(string $value, ServerRequestInterface $request): CookieInterface
{
return Cookie::create(
$this->_config['cookieName'],
$value,
[
'expires' => $this->_config['expiry'] ?: null,
'path' => $request->getAttribute('webroot'),
'secure' => $this->_config['secure'],
'httponly' => $this->_config['httponly'],
'samesite' => $this->_config['samesite'],
]
);
}
}