GHSA-8jqh-95g6-7jpj: CSRF

Summary

Phalcon\Encryption\Crypt provides authenticated encryption: when useSigning is enabled (the default), encrypt() appends an HMAC tag and decrypt() verifies it before returning the plaintext. The verification compares the attacker-supplied tag against the freshly computed HMAC using PHP/Zephir identity comparison (!==), which the Zephir compiler lowers to !ZEPHIRISIDENTICAL(...) — a byte-wise memcmp that returns early on the first differing byte. The comparison time therefore depends on how many leading bytes of the supplied tag are correct, a classic MAC-verification timing side-channel. Every other secret/MAC comparison in the framework uses the constant-time hashequals() (zephirhashequals) — the CSRF token check (Security::checkToken) and the JWT signature check (Signer\Hmac::verify); Crypt::decrypt is the lone deviation.

Details

Vulnerable code

phalcon/Encryption/Crypt.zep:246 (Zephir source):

zephir if true === this->useSigning { // Checks on the decrypted message digest using the HMAC method. if digest !== hashhmac(hashAlgorithm, padded, decryptKey, true) { throw new Mismatch("Hash does not match."); } }

Generated C --> ext/phalcon/encryption/crypt.zep.c:364-367:

c ZEPHIRCALLFUNCTION(&8$$7, "hashhmac", NULL, 245, &hashAlgorithm, &padded, &decryptKey, &$true); ... if (!ZEPHIRISIDENTICAL(&digest, &8$$7)) { // <-- non-constant-time ZEPHIRTHROWEXCEPTIONDEBUGSTR(..., "Hash does not match.", "phalcon/Encryption/Crypt.zep", 247);

ZEPHIRISIDENTICAL --> zephirisidentical() (ext/kernel/operators.c:472) --> Zend isidenticalfunction --> for equal-length strings a memcmp that exits on the first mismatching byte (data-dependent timing).

Impact

The HMAC is the integrity/authentication tag of Phalcon's authenticated-encryption scheme. A successful timing attack (Keyczar/CVE-2009-0654-style: fix the IV+ciphertext so the target tag is constant, then recover it byte-by-byte from response timing) yields a tag the attacker can attach to a chosen IV+ciphertext so that decrypt() accepts it as authentic, defeating the integrity guarantee. Combined with CFB malleability (flipping a ciphertext byte flips the corresponding plaintext byte), an attacker who recovers the forging capability can tamper with the decrypted contents the application trusts (e.g. encrypted cookies carrying authorization/identity state). There is no confidentiality break by itself.

Suggested fix

Replace the identity comparison with the constant-time helper already used elsewhere in the framework. In phalcon/Encryption/Crypt.zep:246:

zephir // before if digest !== hashhmac(hashAlgorithm, padded, decryptKey, true) { throw new Mismatch("Hash does not match."); } // after if true !== hashequals(hashhmac(hashAlgorithm, padded, decryptKey, true), digest) { throw new Mismatch("Hash does not match."); }

hashequals() returns false for unequal-length inputs, so it also covers the truncated-tag case. Optional further hardening: verify the MAC before unpadding (functionally moot here because cryptUnpadText never throws) and consider migrating the default toward an AEAD mode such as aes-256-gcm.

Addressed Issue:

- https://github.com/phalcon/cphalcon/issues/17090

Patched Stream:

- https://github.com/phalcon/cphalcon/issues/17090