ZendFramework Information Disclosure and Insufficient Entropy vulnerability

Summary

In Zend Framework, `Zend_Captcha_Word` (v1) and `Zend\Captcha\Word` (v2) generate a "word" for a CAPTCHA challenge by selecting a sequence of random letters from a character set. Prior to this advisory, the selection was performed using PHP's `internal array_rand()` function. This function does not generate sufficient entropy due to its usage of `rand()` instead of more cryptographically secure methods such as `openssl_pseudo_random_bytes()`. This could potentially lead to information disclosure should an attacker be able to brute force the random number generation.