Server: Apache

Announces web server software and optionally version details.

X-Content-Type-Options: nosniff

A non-standard but widely accepted header introduced originally by Microsoft to disable "content sniffing" or heuristic content type discovery in absence or mismatch of a proper HTTP Content-Type declaration, which led to a number of web attacks. In general, presence of the header with its only defined value of nosniff is considered as part of a properly secured HTTP response.

X-Permitted-Cross-Domain-Policies: none

Header used by Adobe Flash engine to control cross-site access for Flash applications. Most websites not using Flash would prefer to set it with the value of none as an additional precaution against using them in advanced Flash-based XSS vectors. Flash-serving websites can use them to declare the scope of detailed Flash cross-site policies per Adobe specification.

X-XSS-Protection: 1; mode=block

Controls an Cross-Site Scripting (XSS) filters built into the majority of web browsers. The filter is usually turned on by default anyway, but requirement to set the header to 1 became part of canonical set of "secure" HTTP headers. Over time, vulnerabilities in the "sanitizing" mode filter were found, so 1; mode=block became the recommended value. Some companies decided that they don't really need a browser-side XSS filter to mess with their web services which are XSS-free anyway and they became consciously disabling the XSS filter by setting the header to 0.