In Zend Framework 2, the Zend\Math\Rand component generates random bytes using the OpenSSL or Mcrypt extensions when available but will otherwise use PHP's mt_rand() function as a fallback. All outputs from mt_rand() are predictable for the same PHP process if an attacker can brute force the seed used by the Marsenne-Twister algorithm in a Seed Recovery Attack. This attack can be successfully applied with minimum effort if the attacker has access to either a random number from mt_rand() or a Session ID generated without using additional entropy. This makes mt_rand() unsuitable for generating non-trivial random bytes since it has Insufficient Entropy to protect against brute force attacks on the seed.
The Zend\Validate\Csrf component generates CSRF tokens by SHA1 hashing a salt, random number possibly generated using mt_rand() and a form name. Where the salt is known, an attacker can brute force the SHA1 hash with minimum effort to discover the random number when mt_rand() is utilised as a fallback to the OpenSSL and Mcrypt extensions. This constitutes an Information Disclosure where the recovered random number may itself be brute forced to recover the seed value and predict the output of other mt_rand() calls for the same PHP process. This may potentially lead to vulnerabilities in areas of an application where mt_rand() calls exist beyond the scope of Zend Framework.
References
In Zend Framework 2, the
Zend\Math\Randcomponent generates random bytes using the OpenSSL or Mcrypt extensions when available but will otherwise use PHP'smt_rand()function as a fallback. All outputs frommt_rand()are predictable for the same PHP process if an attacker can brute force the seed used by the Marsenne-Twister algorithm in a Seed Recovery Attack. This attack can be successfully applied with minimum effort if the attacker has access to either a random number frommt_rand()or a Session ID generated without using additional entropy. This makesmt_rand()unsuitable for generating non-trivial random bytes since it has Insufficient Entropy to protect against brute force attacks on the seed.The
Zend\Validate\Csrfcomponent generates CSRF tokens by SHA1 hashing a salt, random number possibly generated usingmt_rand()and a form name. Where the salt is known, an attacker can brute force the SHA1 hash with minimum effort to discover the random number whenmt_rand()is utilised as a fallback to the OpenSSL and Mcrypt extensions. This constitutes an Information Disclosure where the recovered random number may itself be brute forced to recover the seed value and predict the output of othermt_rand()calls for the same PHP process. This may potentially lead to vulnerabilities in areas of an application wheremt_rand()calls exist beyond the scope of Zend Framework.References