P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info."

Largely abandoned format for declaring website's privacy policy in machine-readable format. The only reason for many websites to use the header was that old versions of Microsoft Internet Explorer disallowed third-party cookies on websites missing P3P.

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-Frame-Options: SAMEORIGIN

Instructs the browser if the current website can be embedded in HTML frame by another website. Since this allows the parent website to control the framed page, this creates a potential for data theft attacks ("clickjacking") and most sensitive websites won't allow them to be framed at all (deny) or just allow parts of them to be embedded in frames created by themselves only (samesite).

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.

Server: GSE

Announces web server software and optionally version details.

frame-ancestors 'self'

• Policy delivery method: Content-Security-Policy
• Enforcement: True

• No base-uri allows attackers to inject base tags which override the base URI to an attacker-controlled origin. Set to 'none' unless you need to handle tricky relative URLs scheme

• Consider adding block-all-mixed-content directive if your website is only accessible over TLS and you are certain it doesn not have any legacy plaintext resources. Otherwise you may add adding upgrade-insecure-requests directive if your website may still have some legacy plaintext HTTP resources and you want them to be still available rather than blocked