CodeIgniter before 3.0 and Kohana 3.2.3 and earlier and 3.3.x through 3.3.2 make it easier for remote attackers to spoof session cookies and consequently conduct PHP object injection attacks by leveraging use of standard string comparison operators to compare cryptographic hashes.
CodeIgniter before 2.2.0 makes it easier for attackers to decode session cookies by leveraging fallback to a custom XOR-based encryption scheme when the Mcrypt extension for PHP is not available.
system/libraries/Email.php in CodeIgniter before 3.1.3 allows remote attackers to execute arbitrary code by leveraging control over the email->from field to insert sendmail command-line arguments.