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Content security policy

Content Security Policy (CSP) is a W3C specification for instructing the client browser as to which location and/or which type of resources are allowed to be loaded. This spec uses "directives" to define loading behaviors for target resource types. Directives can be specified using HTTP response headers or HTML <meta> tags.

Enabling CSP

Using lusca

lusca is open-source under the Apache license

# In your sails app
npm install lusca --save --save-exact

Then add csp in config/http.js:

// ...

  csp: require('lusca').csp({
    policy: {
      'default-src': '*'
    }
  }),

  // ...

  order: [
    // ...
    'csp',
    // ...
  ]

Supported directives

To give you an idea how this works, here's a snapshot of supported CSP directives, as of 2017:

Directive
default-src	Loading policy for all resources type in case a resource type dedicated directive is not defined (fallback)
script-src	Defines which scripts the protected resource can execute
object-src	Defines from where the protected resource can load plugins
style-src	Defines which styles (CSS) the user applies to the protected resource
img-src	Defines from where the protected resource can load images
media-src	Defines from where the protected resource can load video and audio
frame-src	Defines from where the protected resource can embed frames
font-src	Defines from where the protected resource can load fonts
connect-src	Defines which URIs the protected resource can load using script interfaces
form-action	Defines which URIs can be used as the action of HTML form elements
sandbox	Specifies an HTML sandbox policy that the user agent applies to the protected resource
script-nonce	Defines script execution by requiring the presence of the specified nonce on script elements
plugin-types	Defines the set of plugins that can be invoked by the protected resource by limiting the types of resources that can be embedded
reflected-xss	Instructs a user agent to activate or deactivate any heuristics used to filter or block reflected cross-site scripting attacks, equivalent to the effects of the non-standard X-XSS-Protection header
report-uri	Specifies a URI to which the user agent sends reports about policy violation

For more information, see the W3C CSP Spec.

Browser compatibility

Different CSP response headers are supported by different browsers. For example, Content-Security-Policy is the W3C standard, but various versions of Chrome, Firefox, and IE use X-Content-Security-Policy or X-WebKit-CSP. For the latest information on browser support, see OWasp.

Additional Resources

Content Security Policy (OWasp)
Learn more about installing HTTP middleware in Concepts > Middleware.

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