WebSecurity: Importance of HTTP Headers & In-Depth Security

There is a number of HTTP response headers that you should use to increase the security of your web application. They are referred to as HTTP security headers.

Once implemented, HTTP security headers restrict modern browsers from running into easily preventable vulnerabilities. They also provide yet another, additional layer of security by helping to mitigate security vulnerabilities and prevent attacks (like XSSClickjacking, information leakage, etc.). But it is important to mention that HTTP security headers are not intended to replace proper, secure code.

HTTP STRICT TRANSPORT SECURITY

HTTP Strict Transport Security (HSTS) is a mechanism that prevents user-agents (a browser or any kind of program designed for communication with a particular server) from browsing a website via an unencrypted connection in case an encrypted connection can be established, and only using a trusted certificate.

If the request is communicated through an unencrypted channel, it can be captured and tampered with by an attacker. The attacker then can steal or modify any information transmitted between the client and the server or redirect the user to a phishing website. So, the first goal of HSTS is to ensure traffic is encrypted, so it instructs the browser to always use HTTPS instead of HTTP.

Usually, browsers allow users to ignore TLS errors and continue browsing potentially insecure websites. With HSTS enabled, the user will be unable to skip the browser warning and continue. The second important goal of HSTS is to make sure that the traffic is encrypted using a trusted and valid certificate.

When HSTS response header signals the browser that the certain domain must be requested only using HTTPS, the browser saves this domain to the HSTS list and keeps it there for the timeframe specified in max-age directive of the Strict-Transport-Security header.

There are two cases when HSTS doesn’t provide proper protection:

  • when the user hasn’t browsed to the website before and is making his very first request to this website over HTTP,
  • when existing HSTS data has already expired.

X-XSS-PROTECTION

Some modern browsers have built-in XSS protection mechanisms that can be used as an additional layer of security against Reflected XSS. The main problem with that is that all of the browsers implement built-in XSS filtering differently, so to add more control to the process and make sure that the loading of a page with the malicious content will be blocked, the X-XSS-Protection header is needed.

X-XSS-Protection header is an optional HTTP header that performs XSS filtering by defining the anti-XSS mechanism behavior: from sanitizing the page by blocking injected Javascript to preventing page rendering and reporting the violation.

By default, browsers that support XSS filtering have it enabled. Though it can be disabled, this is considered a bad practice; often, if an application requires XSS protection to be disabled in order to function properly, it is an indication that the application is quite likely vulnerable to XSS.

Please note that only using the X-XSS-Protection header will not protect your application from XSS, but this header will make an important input in your defense-in-depth strategy and make it more robust.

CONTENT-SECURITY-POLICY: X-FRAME-OPTIONS

X-Frame-Options header a defines if the webpage can be rendered inside an <iframe><frame><applet><embed> or <object> tags. Depending on the directive, this header either specifies the list of domains that can embed the webpage, or allows the page to be embedded only inside pages of the same origin, or totally prohibits embedding of a webpage.

The main purpose of the X-Frame-Options header is to protect against ClickjackingClickjacking is an attack when the vulnerable page is loaded in a frame inside the malicious page, and the users are tricked into interaction with buttons and other clickable UI elements (e.g. unknowingly clicking “likes” or downloading malicious files) of a vulnerable page without their knowledge.

Sample Code Snippet

HTTP/1.1 200 OK
Date: Thu, 21 Mar 2019 09:05:07 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 0
Connection: close
Cache-Control: max-age=600
Content-Security-Policy: script-src 'self' *.followcybersecurity.com 'unsafe-inline' 'unsafe-eval'  www.google-analytics.com; img-src 'self' *.followcybersecurity.com
Expires: Thu, 21 Mar 2019 09:15:06 GMT
Location: https://followcybersecurity.com
strict-transport-security: max-age=31536000
Vary: Accept-Language, Accept-Encoding
x-content-type-options: nosniff
X-Frame-Options: DENY
X-Robots-Tag: noodp
x-xss-protection: 1; mode=block  

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