CodeIgniter is a PHP full-stack web framework. Prior to 4.5.8, CodeIgniter lacked proper header validation for its name and value. The potential attacker can construct deliberately malformed headers with Header class. This could disrupt application functionality, potentially causing errors or generating invalid HTTP requests. In some cases, these malformed requests might lead to a DoS scenario if a remote service’s web application firewall interprets them as malicious and blocks further communication with the application. This vulnerability is fixed in 4.5.8.