This document discusses exploiting vulnerabilities related to HTTP host header tampering. It notes that tampering with the host header can lead to issues like password reset poisoning, cache poisoning, and cross-site scripting. It provides examples of how normal host header usage can be tampered with, including by spoofing the header to direct traffic to malicious sites. The document also lists some potential victims of host header attacks, like Drupal, Django and Joomla, and recommends developers check settings to restrict allowed hosts. It proposes methods for bruteforcing subdomains and host headers to find vulnerabilities.