Description
This script is vulnerable to CRLF injection attacks.
HTTP headers have the structure "Key: Value", where each line is separated by the CRLF combination. If the user input is injected into the value section without properly escaping/removing CRLF characters it is possible to alter the HTTP headers structure.
HTTP Response Splitting is a new application attack technique which enables various new attacks such as web cache poisoning, cross user defacement, hijacking pages with sensitive user information and cross-site scripting (XSS). The attacker sends a single HTTP request that forces the web server to form an output stream, which is then interpreted by the target as two HTTP responses instead of one response.
Remediation
You need to restrict CR(0x13) and LF(0x10) from the user input or properly encode the output in order to prevent the injection of custom HTTP headers.