List of useful HTTP headers

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This page lists useful security-related HTTP headers. In most architectures these headers can be set in web server configuration (Apache, IIS), without changing actual application's code. This offers significantly faster and cheaper method for at least partial mitigation of existing issues, and an additional layer of defense for new applications.

Field name Description Example
Strict-Transport-Security Enforces secure (HTTP over SSL/TLS) connections to the server. This reduces impact of bugs in web applications leaking session data through cookies and external links. Strict-Transport-Security: max-age=16070400; includeSubDomains
X-Frame-Options, Frame-Options Clickjacking protection. Values: deny - no rendering within a frame, sameorigin - no rendering if origin mismatch, allow-from: URL - allow rendering frame if loaded from URL X-Frame-Options: deny
X-XSS-Protection This header enables the Cross-site scripting (XSS) filter built into most recent web browsers. It's usually enabled by default anyway, so the role of this header is to re-enable the filter for this particular website if it was disabled by the user. This header is supported in IE 8+, and in Chrome (not sure which versions). The anti-XSS filter was added in Chrome 4. Its unknown if that version honored this header. X-XSS-Protection: 1; mode=block
X-Content-Type-Options The only defined value, "nosniff", prevents Internet Explorer and Google Chrome from MIME-sniffing a response away from the declared content-type. This also applies to Google Chrome, when downloading extensions. This reduces exposure to drive-by download attacks and sites serving user uploaded content that, by clever naming, could be treated by MSIE as executable or dynamic HTML files. X-Content-Type-Options: nosniff
X-Content-Security-Policy, X-WebKit-CSP Content Security Policy definition. Requires careful tuning and precise definition of the policy. If enabled CSP has significant impact on the way browser renders pages (e.g. inline JavaScript disabled by default and must be explicitly allowed in policy). CSP prevents a wide range of attacks, including Cross-site Scripting and other cross-site injections. X-WebKit-CSP: default-src 'self'


Real life examples

Below examples present selected HTTP headers as set by popular websites to demonstrate that they are indeed being used in production services:


As of January 2013 Facebook main page was setting these security related HTTP headers.

Strict-Transport-Security: max-age=60
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
X-WebKit-CSP: default-src *; script-src https://*
  http://* https://* http://* *
  * * ** **
  'unsafe-inline' 'unsafe-eval' https://* http://*;
  style-src * 'unsafe-inline'; connect-src https://* http://*
  https://* http://* * **
  https://* ws://** http://*;
X-XSS-Protection: 1; mode=block

Especially interesting is Facebook's use of Content Security Policy (using Google Chrome syntax), whose implementation can be challenging for large sites with heavy usage of JavaScript.


As of January 2013 Google+ main page was setting these security related HTTP headers:

x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block


As of May 2013 Twitter main page was setting these security related HTTP headers:

strict-transport-security: max-age=631138519
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block