Date: Tue, 19 Jul 2016 00:56:58 -0400 From: Scott Arciszewski <scott@...agonie.com> To: fulldisclosure@...lists.org, oss-security@...ts.openwall.com Subject: Ruining the Magic of Magento's Encryption Library Hello mcrypt, my old friend I've come to exploit you again Because a version slowly rotting Is well-deserved for a boycotting And the S-box that was planted in its GOST Still remains Within the sound of silence ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ 8< ~ Let's talk about Magento. The Wikipedia page for Magento begins, "Magento is an open-source e-commerce platform written in PHP." This bears emphasis: e-commerce platform. When I hear e-commerce, I think "financial information". I think "credit card numbers" and "probably PCI-DSS violations should anything be obviously stupid". Let's look at how Magento implements cryptography, with a series of exhibits followed by an explanation of what's happening and why it's dangerous: A. https://github.com/magento/magento2/blob/6ea7d2d85cded3fa0fbcf4e7aa0dcd4edbf568a6/lib/internal/Magento/Framework/Encryption/Encryptor.php#L268-L320 B. https://github.com/magento/magento2/blob/6ea7d2d85cded3fa0fbcf4e7aa0dcd4edbf568a6/lib/internal/Magento/Framework/Encryption/Encryptor.php#L390-L399 C. https://github.com/magento/magento2/blob/6ea7d2d85cded3fa0fbcf4e7aa0dcd4edbf568a6/lib/internal/Magento/Framework/Encryption/Crypt.php#L63-L77 D. https://github.com/magento/magento2/blob/6ea7d2d85cded3fa0fbcf4e7aa0dcd4edbf568a6/lib/internal/Magento/Framework/Encryption/Encryptor.php#L170 If you looked at the code, I promise this is every bit as bad as it looks at a glance. EXHIBIT A ========= Magento's decryption expects up to 4 strings concatenated by a : character. Depending on the number of pieces, it assumes a totally different setup: 1 piece: Blowfish, in ECB mode! 2 or 3 pieces: Probably blowfish, but maybe AES or Rijndael-256, depending on the integer supplied by the attacker. 4 pieces: We finally get an initialization vector, which means CBC mode can be used. At no point do they authenticate _anything_, so no matter what: - You get to control which branch is selected by breaking pieces off the attacker-chosen message. - You get to choose the ciphertext that the attempted decryption is performed upon. EXHIBIT B ========= If you thought the ability to be encrypted with AES was a saving grace, too bad. They hard-code your choice to ECB mode. The only way you can get CBC mode (which, again, is unauthenticated) is to use the non-standard Rijndael256 cipher. EXHIBIT C ========= If you thought it couldn't possibly get any worse, Magento's encryption library will either: - Give you an IV consisting entirely of NULL bytes. - Generate it, using rand(), on a 62-character keyspace. (Y'know, because it's not XORed with the plaintext in CBC mode and biases aren't a concern or anything.) EXHIBIT D ========= Yes, that is how Magento hashes passwords. Which is weird: They go out of their way to compare strings in constant-time, but PUTTING IT ALL TOGETHER ======================= An attacker has a great deal of control over the ciphertext, and incidentally which cipher mode is used by the decryption routine. Nothing is authenticated. At all. ECB mode everywhere. When CBC mode is actually used, it's used with a laughably weak IV and a non-standard cipher. Also, unauthenticated. Magento, one of the largest open source e-commerce platforms, ships a broken cryptography library that clueless developers are probably using to encrypt your credit card information for their client's customers. Given the prevalence of ECB mode, and the weak IV used in CBC mode, you should assume anything you encrypted with Magento's encryption library is both: - Decryptable, if an attacker can alter plaintexts or ciphertexts and study the output of either operation, without the key - Forgeable This cryptography implementation is very irresponsible and, because cryptography is involved, warrants immediate full disclosure so everyone can cease to use their broken crypto as soon as possible. If you need a remediation strategy, I've got you covered: https://paragonie.com/blog/2015/11/choosing-right-cryptography-library-for-your-php-project-guide Scott Arciszewski Chief Development Officer Paragon Initiative Enterprises <https://paragonie.com>
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