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Vapor Security Headers

Language Build Status Code Coverage MIT License

A Middleware library for adding security headers to your Vapor application.

Features

Easily add headers to all your responses for improving the security of your site for you and your users. Currently supports:

  • Content-Security-Policy
  • Content-Security-Policy-Report-Only
  • X-XSS-Protection
  • X-Frame-Options
  • X-Content-Type-Options
  • Strict-Transport-Security (HSTS)
  • Redirect HTTP to HTTPS
  • Server
  • Referrer Policy

These headers will help prevent cross-site scripting attacks, SSL downgrade attacks, content injection attacks, click-jacking etc. They will not help for any attacks directly against your server, but they will help your users and help secure sensitive information (CSRF tokens). Please note that this library does not guarantee anything and nothing is ever completely secure.

Usage

Add the package

Add the package as a dependency in your Package.swift manifest:

dependencies: [
    ...,
    .package(url: "https://github.com/brokenhandsio/VaporSecurityHeaders.git", from: "3.0.0")
]

Then add the dependency to your target:

.target(name: "App",
        dependencies: [
                // ...
                "VaporSecurityHeaders"]),

Configuration

To use Vapor Security Headers, you need to add the middleware to your Application's Middlewares. Vapor Security Headers makes this easy to do with a build function on the factory. Note: if you want security headers added to error reponses (recommended), you need to initialise the Middlewares from fresh and add the middleware in after the SecuriyHeaders. In configure.swift add:

let securityHeadersFactory = SecurityHeadersFactory()

application.middleware = Middlewares()
application.middleware.use(securityHeadersFactory.build())
application.middleware.use(ErrorMiddleware.default(environment: application.environment))
// Add other middlewares...

The default factory will add default values to your site for Content-Security-Policy, X-XSS-Protection, X-Frame-Options and X-Content-Type-Options.

x-content-type-options: nosniff
content-security-policy: default-src 'self'
x-frame-options: DENY
x-xss-protection: 0

Note: You should ensure you set the security headers as the first middleware in your Middlewares (i.e., the first middleware to be applied to responses) to make sure the headers get added to all responses.

If you want to add your own values, it is easy to do using the factory. For instance, to add a content security policy configuration, just do:

let cspValue = "default-src 'none'; script-src https://static.brokenhands.io;"

let cspConfig = ContentSecurityPolicyConfiguration(value: cspValue)

let securityHeadersFactory = SecurityHeadersFactory().with(contentSecurityPolicy: cspConfig)
application.middleware.use(securityHeadersFactory.build())
x-content-type-options: nosniff
content-security-policy: default-src 'none'; script-src https://static.brokenhands.io;
x-frame-options: DENY
x-xss-protection: 0

Each different header has its own configuration and options, details of which can be found below.

You can test your site by visiting the awesome Security Headers (no affiliation) website.

API Headers

If you are running an API you can choose a default configuration for that by creating it with:

let securityHeaders = SecurityHeadersFactory.api()
application.middleware.use(securityHeaders.build())
x-content-type-options: nosniff
content-security-policy: default-src 'none'
x-frame-options: DENY
x-xss-protection: 0

Server Configuration

Vapor

If you are running Vapor on it's own (i.e. not as a CGI application or behind a reverse proxy) then you do not need to do anything more to get it running!

Nginx, Apache and 3rd Party Services

Both web servers should pass on the response headers from Vapor without issue when running as a reverse proxy. Some servers and providers (such as Heroku) will inject their own headers or block certain headers (such as HSTS to stop you locking out their whole site). You will need to check with your provider to see what is enabled and allowed.

Security Header Information

Content-Security-Policy

Content Security Policy is one of the most effective tools for protecting against cross-site scripting attacks. In essence it is a way of whitelisting sources for content so that you only load from known and trusted sources. For more information about CSP, read Scott Helme's awesome blog post which tells you how to configure it and what to use.

The Vapor Security Headers package will set a default CSP of default-src: 'self', which means that you can load images, scripts, fonts, CSS etc only from your domain. It also means that you cannot have any inline Javascript or CSS, which is one of the most effective measures you can take in protecting your site, and will wipe out a large proportion of content-injection attacks.

The API default CSP is default-src: 'none' as an API should only return data and never be loading scripts or images to display!

You can build a CSP header (ContentSecurityPolicy) with the following directives:

  • baseUri(sources)
  • blockAllMixedContent()
  • connectSrc(sources)
  • defaultSrc(sources)
  • fontSrc(sources)
  • formAction(sources)
  • frameAncestors(sources)
  • frameSrc(sources)
  • imgSrc(sources)
  • manifestSrc(sources)
  • mediaSrc(sources)
  • objectSrc(sources)
  • pluginTypes(types)
  • reportTo(json_object)
  • reportUri(uri)
  • requireSriFor(values)
  • sandbox(values)
  • scriptSrc(sources)
  • styleSrc(sources)
  • upgradeInsecureRequests()
  • workerSrc(sources)

Example:

let cspConfig = ContentSecurityPolicy()
        .scriptSrc(sources: "https://static.brokenhands.io")
        .styleSrc(sources: "https://static.brokenhands.io")
        .imgSrc(sources: "https://static.brokenhands.io")
Content-Security-Policy: script-src https://static.brokenhands.io; style-src https://static.brokenhands.io; img-src https://static.brokenhands.io

You can set a custom header with ContentSecurityPolicy().set(value) or ContentSecurityPolicyConfiguration(value).

ContentSecurityPolicy().set(value)

let cspBuilder = ContentSecurityPolicy().set(value: "default-src: 'none'")

let cspConfig = ContentSecurityPolicyConfiguration(value: cspBuilder)

let securityHeadersFactory = SecurityHeadersFactory().with(contentSecurityPolicy: cspConfig)

ContentSecurityPolicyConfiguration(value)

let cspConfig = ContentSecurityPolicyConfiguration(value: "default-src 'none'")

let securityHeadersFactory = SecurityHeadersFactory().with(contentSecurityPolicy: cspConfig)
Content-Security-Policy: default-src: 'none'

The following CSP keywords (CSPKeywords) are also available to you:

  • CSPKeywords.all = *
  • CSPKeywords.none = 'none'
  • CSPKeywords.`self` = 'self'
  • CSPKeywords.strictDynamic = 'strict-dynamic'
  • CSPKeywords.unsafeEval = 'unsafe-eval'
  • CSPKeywords.unsafeHashedAttributes = 'unsafe-hashed-attributes'
  • CSPKeywords.unsafeInline = 'unsafe-inline'

Example:

CSPKeywords.`self` // “‘self’”
ContentSecurityPolicy().defaultSrc(sources: CSPKeywords.`self`)
Content-Security-Policy: default-src 'self'

You can also utilize the Report-To directive:

let reportToEndpoint = CSPReportToEndpoint(url: "https://csp-report.brokenhands.io/csp-reports")

let reportToValue = CSPReportTo(group: "vapor-csp", max_age: 10886400, endpoints: [reportToEndpoint], include_subdomains: true)

let cspValue = ContentSecurityPolicy()
    .defaultSrc(sources: CSPKeywords.none)
    .scriptSrc(sources: "https://static.brokenhands.io")
    .reportTo(reportToObject: reportToValue)
Content-Security-Policy: default-src 'none'; script-src https://static.brokenhands.io; report-to {"group":"vapor-csp","endpoints":[{"url":"https:\/\/csp-report.brokenhands.io\/csp-reports"}],"include_subdomains":true,"max_age":10886400}

See Google Developers - The Reporting API for more information on the Report-To directive.

Content Security Policy Configuration

To configure your CSP you can add it to your ContentSecurityPolicyConfiguration like so:

let cspBuilder = ContentSecurityPolicy()
    .defaultSrc(sources: CSPKeywords.none)
    .scriptSrc(sources: "https://static.brokenhands.io")
    .styleSrc(sources: "https://static.brokenhands.io")
    .imgSrc(sources: "https://static.brokenhands.io")
    .fontSrc(sources: "https://static.brokenhands.io")
    .connectSrc(sources: "https://*.brokenhands.io")
    .formAction(sources: CSPKeywords.`self`)
    .upgradeInsecureRequests()
    .blockAllMixedContent()
    .requireSriFor(values: "script", "style")
    .reportUri(uri: "https://csp-report.brokenhands.io")

let cspConfig = ContentSecurityPolicyConfiguration(value: cspBuilder)

let securityHeadersFactory = SecurityHeadersFactory().with(contentSecurityPolicy: cspConfig)
Content-Security-Policy: default-src 'none'; script-src https://static.brokenhands.io; style-src https://static.brokenhands.io; img-src https://static.brokenhands.io; font-src https://static.brokenhands.io; connect-src https://*.brokenhands.io; form-action 'self'; upgrade-insecure-requests; block-all-mixed-content; require-sri-for script style; report-uri https://csp-report.brokenhands.io

This policy means that by default everything is blocked, however:

  • Scripts can be loaded from https://static.brokenhands.io
  • CSS can be loaded from https://static.brokenhands.io
  • Images can be loaded from https://static.brokenhands.io
  • Fonts can be loaded from https://static.brokenhands.io
  • Any JS connections can only be made to any brokenhands.io subdomain over HTTPS
  • Form actions go only go to the same site
  • Any HTTP requests will be sent over HTTPS
  • Any attempts to load HTTP content will be blocked
  • Any scripts and style links must have SRI values
  • Any policy violations will be sent to https://csp-report.brokenhands.io

Check out https://report-uri.io/ for a free tool to send all of your CSP reports to.

Page Specific CSP

Vapor Security Headers also supports setting the CSP on a route or request basis. If the middleware has been added to the Middlewares, you can override the CSP for a request. This allows you to have a strict default CSP, but allow content from extra sources when required, such as only allowing the Javascript for blog comments on the blog page. Create a separate ContentSecurityPolicyConfiguration and then add it to the request. For example, inside a route handler, you could do:

let cspConfig = ContentSecurityPolicy()
    .defaultSrc(sources: CSPKeywords.none)
    .scriptSrc(sources: "https://comments.disqus.com")

let pageSpecificCSP = ContentSecurityPolicyConfiguration(value: cspConfig)
req.contentSecurityPolicy = pageSpecificCSP
content-security-policy: default-src 'none'; script-src https://comments.disqus.com

Content-Security-Policy-Report-Only

Content-Security-Policy-Report-Only works in exactly the same way as Content-Security-Policy except that any violations will not block content, but they will be reported back to you. This is extremely useful for testing a CSP before rolling it out over your site. You can run both side by side - so for example have a fairly simply policy under Content-Security-Policy but test a more restrictive policy over Content-Security-Policy-Report-Only. The great thing about this is that your users do all your testing for you!

To configure this, just pass in your policy to the ContentSecurityPolicyReportOnlyConfiguration:

let cspConfig = ContentSecurityPolicyReportOnlyConfiguration(value: "default-src https:; report-uri https://csp-report.brokenhands.io")
        
let securityHeadersFactory = SecurityHeadersFactory().with(contentSecurityPolicyReportOnly: cspConfig)  
content-security-policy-report-only: default-src https:; report-uri https://csp-report.brokenhands.io

The above blog post goes into more details about this.

X-XSS-Protection

X-XSS-Protection configures the browser's cross-site scripting filter. This package configures the header to be disabled, which (surprisingly) offers security benefits. See this article on MDN for more information.

let xssProtectionConfig = XSSProtectionConfiguration()
    
let securityHeadersFactory = SecurityHeadersFactory().with(XSSProtection: xssProtectionConfig)
x-xss-protection: 0

X-Content-Type-Options

X-Content-Type-Options stops a browser from trying to MIME-sniff content types from requests and makes sure that the declared content type is used. It only has one option, which is nosniff. To use this, set your ContentTypeOptionsConfiguration as so (this is set by default on any SecurityHeaders object):

let contentTypeConfig = ContentTypeOptionsConfiguration(option: .nosniff)
    
let securityHeadersFactory = SecurityHeadersFactory().with(contentTypeOptions: contentTypeConfig)
x-content-type-options: nosniff

To disable it:

let contentTypeConfig = ContentTypeOptionsConfiguration(option: .none)

X-Frame-Options

The X-Frame-Options header is for click-jacking attacks and tells the browser whether your site can be framed. To stop your site from being framed completely (the default setting):

let frameOptionsConfig = FrameOptionsConfiguration(option: .deny)

let securityHeadersFactory = SecurityHeadersFactory().with(frameOptions: frameOptionsConfig)
x-frame-options: DENY

To allow you to frame your own site:

let frameOptionsConfig = FrameOptionsConfiguration(option: .sameOrigin)
x-frame-options: SAMEORIGIN

To allow a specific site to frame yours, use:

let frameOptionsConfig = FrameOptionsConfiguration(option: .allow(from: "https://mytrustedsite.com"))
x-frame-options: ALLOW-FROM https://mytrustedsite.com

Strict-Transport-Security

Strict-Transport-Security is an improvement over 301/302 redirects or HTTPS forwarding. Browsers will default to HTTP when you navigate to an address but HSTS (HTTP Strict Transport Security) tells the browser that it should always connect over HTTPS, so all future requests will be HTTPS, even if you click on an HTTP link. By default this is not turned on with the Security Headers library as it can cause issues if you haven't got HTTPS set up properly. If you specify this header and then at a future date you don't renew your SSL certificate or disable SSL then the browser will refuse to load your site! However, it is highly recommended as it ensures that all connections are over HTTPS, even if a user clicks on an HTTP link.

The default configuration is max-age=31536000; includeSubDomains; preload. This tells the browser to force HTTPS for a year, and for every subdomain as well. So if you specify this, make sure you have SSL properly configured for all subdomains, e.g. test.mysite.com, dev.mysite.com etc.

The preload tag tells Chrome that you want to be preloaded. This will add you to the preload list, which means that the browser will automatically know you want an HTTPS connection before you have even visited the site, so removes the initial HTTP handshake the first time you specify the header. However, this has now been superseded and you should now submit your site at https://hstspreload.org. This will add your site to Chrome's source to preload it in the future and it is the list that other browsers use as well. Note that it is difficult to remove yourself from the list (and can take months to get it rolled out to the browsers), so by submitting your site you are effectively guaranteeing working HTTPS for the rest of the life of your site. However, these days it shouldn't be a problem - use Let's Encrypt! Note: You should be careful about using this on deployment sites such as Heroku as it may cause issues.

To use the Strict-Transport-Security header, you can configure and add it as so (default values are shown):

let strictTransportSecurityConfig = StrictTransportSecurityConfiguration(maxAge: 31536000, includeSubdomains: true, preload: true)

let securityHeadersFactory = SecurityHeadersFactory().with(strictTransportSecurity: strictTransportSecurityConfig)
strict-transport-security: max-age=31536000; includeSubDomains; preload

Redirect HTTP to HTTPS

If Strict-Transport-Security is not enough to accomplish a forwarding connection to HTTPS from the browsers, you can opt to add an additional middleware who provides this redirection if clients try to reach your site with an HTTP connection.

To use the HTTPS Redirect Middleware, you can add the following line in configure.swift to enable the middleware. This must be done before securityHeadersFactory.build() to ensure HSTS works:

app.middleware.use(HTTPSRedirectMiddleware())

The HTTPSRedirectMiddleware allows you to set an array of allowed hosts that the application can redirect to. This prevents attackers poisoning the Host header and forcing a redirect to a domain under their control. To use this, provide the list of allowed hosts to the initialiser:

app.middleware.use(HTTPSRedirectMiddleware(allowedHosts: ["www.brokenhands.io", "brokenhands.io", "static.brokenhands.io"))

Any attempts to redirect to another host, for example attacker.com will result in a 400 Bad Request response.

Server

The Server header is usually hidden from responses in order to not give away what type of server you are running and what version you are using. This is to stop attackers from scanning your site and using known vulnerabilities against it easily. By default Vapor does not show the server header in responses for this reason.

However, it can be fun to add in a custom server configuration for a bit of personalization, such as your website name, or company name (look at Github's response) and the ServerConfiguraiton allows this. So, for example, if I wanted my Server header to be brokenhands.io, I would configure it like:

let serverConfig = ServerConfiguration(value: "brokenhands.io")

let securityHeadersFactory = SecurityHeadersFactory().with(server: serverConfig)
server: brokenhands.io

Referrer Policy

The Referrer Policy is the latest header to have been introduced (the spec can be found here). It basically defines when the Referrer header can be sent with a request. You may want to not send the header when going from HTTPS to HTTP for example.

The different options are:

  • ""
  • "no-referrer"
  • "no-referrer-when-downgrade"
  • "same-origin"
  • "origin"
  • "strict-origin"
  • "origin-when-cross-origin"
  • "strict-origin-when-cross-origin"
  • "unsafe-url"

I won't go into details about each one, I will point you in the direction of a far better explanation by Scott Helme.

let referrerPolicyConfig = ReferrerPolicyConfiguration(.noReferrer)

let securityHeadersFactory = SecurityHeadersFactory().with(referrerPolicy: referrerPolicyConfig)
referrer-policy: no-referrer

You can also set a fallback policy.

let referrerPolicyConfig = ReferrerPolicyConfiguration([.noReferrer, .strictOriginWhenCrossOrigin])

let securityHeadersFactory = SecurityHeadersFactory().with(referrerPolicy: referrerPolicyConfig)
referrer-policy: no-referrer, strict-origin-when-cross-origin