symfony-standard-headers-csrf-bundle

Table of contents

• Overview
  • How it works?
• Installation and requirements
• Configuration
• Public api

Overview

Protect symfony applications against CSRF attacks with the help of standard headers.

The mechanism to prevent CSRF attacks which is used by this bundle can best be read under OWASP. The technique is named "Verifying Origin With Standard Headers".

How it works?

This bundle is based on the headers Host, Origin and Referer. They're part of the forbidden headers and cannot be changed programmatically with a standard browser. Please read the OWASP page carefully as this technique may not work in all cases.

This bundle returns a status code 403 if the request isn't safe. A request is safe if at least one of the following criteria is met:

• the http method is a safe http method.
• the request path matches one of the allowed_paths from the configuration.
• the origin header matches the Host header or one of the allowed_origins from the configuration.
• fallback_to_referer is enabled and the Referer header matches the Host header or one of the allowed_origins from the configuration.
• allow_null_origin is enabled and the Origin header is equal to "null".

If there're trusted proxies configured in your symfony application, X-Forwarded-Host is used instead of Host.

Installation and requirements

Add the bundle to your project.

composer require marein/symfony-standard-headers-csrf-bundle

Add the bundle in the kernel. This can be different for your setup.

public function registerBundles()
{
    return [
        // ...
        new \Marein\StandardHeadersCsrfBundle\MareinStandardHeadersCsrfBundle(),
        // ...
    ];
}

Configuration

This is an example of all configurations in yaml format.

marein_standard_headers_csrf:
    # List of regular expressions that are used to check for allowed request paths.
    # Each entry is automatically surrounded by the delimiter #.
    #
    # Type: string[]
    # Default: []
    allowed_paths:
        - '^/api'

    # List of regular expressions that are used to check for allowed origins.
    # Each entry is automatically surrounded by the delimiter #.
    #
    # Type: string[]
    # Default: []
    allowed_origins:
        - '^https?://my-domain\.com$'
        - '^https?://.*\.my-other-domain-including-subdomains\.com$'

    # Switch to enable the comparison of the host header and allowed_origins with the referer header.
    #
    # Type: bool
    # Default: true
    fallback_to_referer: true

    # Switch to allow "null" as a valid origin header value.
    #
    # Type: bool
    # Default: false
    allow_null_origin: false

Public api

Only the bundle configuration is part of the public api. Everything else can change and is not considered a breaking change. Please don't use classes or services directly.