CRLF injection vulnerability in the drupal_set_header function in Drupal 6.x before 6.38, when used with PHP before 5.1.2, allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks by leveraging a module that allows user-submitted data to appear in HTTP headers. <a href="https://cwe.mitre.org/data/definitions/93.html">CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')</a>