Merge pull request #598 from xxyy/feature/csp

Implement basic CSP support

12 files changed, 132 insertions, 15 deletions

diff --git a/README.md b/README.md
index 1e7d79ab..fb1f8e3d 100644
--- a/README.md
+++ b/README.md
@@ -197,6 +197,7 @@ There are some configs you need to change in the files below
 | HMD_HSTS_INCLUDE_SUBDOMAINS | `true` | set to include subdomains in HSTS (default is `true`) |
 | HMD_HSTS_MAX_AGE | `31536000` | max duration in seconds to tell clients to keep HSTS status (default is a year) |
 | HMD_HSTS_PRELOAD | `true` | whether to allow preloading of the site's HSTS status (e.g. into browsers) |
+| HMD_CSP_ENABLE | `true` | whether to enable Content Security Policy (directives cannot be configured with environment variables) |
 
 ## Application settings `config.json`
 
@@ -208,7 +209,8 @@ There are some configs you need to change in the files below
 | port | `80` | web app port |
 | alloworigin | `['localhost']` | domain name whitelist |
 | usessl | `true` or `false` | set to use ssl server (if true will auto turn on `protocolusessl`) |
-| hsts | `{"enable": "true", "maxAgeSeconds": "31536000", "includeSubdomains": "true", "preload": "true"}` | [HSTS](https://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security) options to use with HTTPS (default is the example value, max age is a year) |
+| hsts | `{"enable": true, "maxAgeSeconds": 31536000, "includeSubdomains": true, "preload": true}` | [HSTS](https://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security) options to use with HTTPS (default is the example value, max age is a year) |
+| csp | `{"enable": true, "directives": {"scriptSrc": "trustworthy-scripts.example.com"}, "upgradeInsecureRequests": "auto", "addDefaults": true}` | Configures [Content Security Policy](https://helmetjs.github.io/docs/csp/). Directives are passed to Helmet - see [their documentation](https://helmetjs.github.io/docs/csp/) for more information on the format. Some defaults are added to the configured values so that the application doesn't break. To disable this behaviour, set `addDefaults` to `false`. Further, if `usecdn` is on, some CDN locations are allowed too. By default (`auto`), insecure (HTTP) requests are upgraded to HTTPS via CSP if `usessl` is on. To change this behaviour, set `upgradeInsecureRequests` to either `true` or `false`. |
 | protocolusessl | `true` or `false` | set to use ssl protocol for resources path (only applied when domain is set) |
 | urladdport | `true` or `false` | set to add port on callback url (port 80 or 443 won't applied) (only applied when domain is set) |
 | usecdn | `true` or `false` | set to use CDN resources or not (default is `true`) |
diff --git a/app.js b/app.js
index 37e772bc..2183b149 100644
--- a/app.js
+++ b/app.js
@@ -24,6 +24,7 @@ var config = require('./lib/config')
 var logger = require('./lib/logger')
 var response = require('./lib/response')
 var models = require('./lib/models')
+var csp = require('./lib/csp')
 
 // generate front-end constants by template
 var constpath = path.join(__dirname, './public/js/lib/common/constant.ejs')
@@ -108,6 +109,19 @@ if (config.hsts.enable) {
   logger.info('https://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security')
 }
 
+// Generate a random nonce per request, for CSP with inline scripts
+app.use(csp.addNonceToLocals)
+
+// use Content-Security-Policy to limit XSS, dangerous plugins, etc.
+// https://helmetjs.github.io/docs/csp/
+if (config.csp.enable) {
+  app.use(helmet.contentSecurityPolicy({
+    directives: csp.computeDirectives()
+  }))
+} else {
+  logger.info('Content-Security-Policy is disabled. This may be a security risk.')
+}
+
 i18n.configure({
   locales: ['en', 'zh', 'zh-CN', 'zh-TW', 'fr', 'de', 'ja', 'es', 'ca', 'el', 'pt', 'it', 'tr', 'ru', 'nl', 'hr', 'pl', 'uk', 'hi', 'sv', 'eo', 'da'],
   cookie: 'locale',
diff --git a/config.json.example b/config.json.example
index c2c270c3..f5ddf182 100644
--- a/config.json.example
+++ b/config.json.example
@@ -17,10 +17,17 @@
     "production": {
         "domain": "localhost",
         "hsts": {
-            "enable": "true",
+            "enable": true,
             "maxAgeSeconds": "31536000",
-            "includeSubdomains": "true",
-            "preload": "true"
+            "includeSubdomains": true,
+            "preload": true
+        },
+        csp: {
+            "enable": true,
+            "directives": {
+            },
+            "upgradeInsecureRequests": "auto"
+            "addDefaults": true
         },
         "db": {
             "username": "",
diff --git a/lib/config/default.js b/lib/config/default.js
index 000c154a..ec7c7451 100644
--- a/lib/config/default.js
+++ b/lib/config/default.js
@@ -13,6 +13,13 @@ module.exports = {
     includeSubdomains: true,
     preload: true
   },
+  csp: {
+    enable: true,
+    directives: {
+    },
+    addDefaults: true,
+    upgradeInsecureRequests: 'auto'
+  },
   protocolusessl: false,
   usecdn: true,
   allowanonymous: true,
diff --git a/lib/config/environment.js b/lib/config/environment.js
index eedd4913..24a85d65 100644
--- a/lib/config/environment.js
+++ b/lib/config/environment.js
@@ -14,6 +14,9 @@ module.exports = {
     includeSubdomains: toBooleanConfig(process.env.HMD_HSTS_INCLUDE_SUBDOMAINS),
     preload: toBooleanConfig(process.env.HMD_HSTS_PRELOAD)
   },
+  csp: {
+    enable: toBooleanConfig(process.env.HMD_CSP_ENABLE)
+  },
   protocolusessl: toBooleanConfig(process.env.HMD_PROTOCOL_USESSL),
   alloworigin: toArrayConfig(process.env.HMD_ALLOW_ORIGIN),
   usecdn: toBooleanConfig(process.env.HMD_USECDN),
diff --git a/lib/csp.js b/lib/csp.js
new file mode 100644
index 00000000..509bc530
--- /dev/null
+++ b/lib/csp.js
@@ -0,0 +1,80 @@
+var config = require('./config')
+var uuid = require('uuid')
+
+var CspStrategy = {}
+
+var defaultDirectives = {
+  defaultSrc: ['\'self\''],
+  scriptSrc: ['\'self\'', 'vimeo.com', 'https://gist.github.com', 'www.slideshare.net', 'https://query.yahooapis.com', 'https://*.disqus.com', '\'unsafe-eval\''],
+  // ^ TODO: Remove unsafe-eval - webpack script-loader issues https://github.com/hackmdio/hackmd/issues/594
+  imgSrc: ['*'],
+  styleSrc: ['\'self\'', '\'unsafe-inline\'', 'https://assets-cdn.github.com'], // unsafe-inline is required for some libs, plus used in views
+  fontSrc: ['\'self\'', 'https://public.slidesharecdn.com'],
+  objectSrc: ['*'], // Chrome PDF viewer treats PDFs as objects :/
+  childSrc: ['*'],
+  connectSrc: ['*']
+}
+
+var cdnDirectives = {
+  scriptSrc: ['https://cdnjs.cloudflare.com', 'https://cdn.mathjax.org'],
+  styleSrc: ['https://cdnjs.cloudflare.com', 'https://fonts.googleapis.com'],
+  fontSrc: ['https://cdnjs.cloudflare.com', 'https://fonts.gstatic.com']
+}
+
+CspStrategy.computeDirectives = function () {
+  var directives = {}
+  mergeDirectives(directives, config.csp.directives)
+  mergeDirectivesIf(config.csp.addDefaults, directives, defaultDirectives)
+  mergeDirectivesIf(config.usecdn, directives, cdnDirectives)
+  if (!areAllInlineScriptsAllowed(directives)) {
+    addInlineScriptExceptions(directives)
+  }
+  addUpgradeUnsafeRequestsOptionTo(directives)
+  return directives
+}
+
+function mergeDirectives (existingDirectives, newDirectives) {
+  for (var propertyName in newDirectives) {
+    var newDirective = newDirectives[propertyName]
+    if (newDirective) {
+      var existingDirective = existingDirectives[propertyName] || []
+      existingDirectives[propertyName] = existingDirective.concat(newDirective)
+    }
+  }
+}
+
+function mergeDirectivesIf (condition, existingDirectives, newDirectives) {
+  if (condition) {
+    mergeDirectives(existingDirectives, newDirectives)
+  }
+}
+
+function areAllInlineScriptsAllowed (directives) {
+  return directives.scriptSrc.indexOf('\'unsafe-inline\'') !== -1
+}
+
+function addInlineScriptExceptions (directives) {
+  directives.scriptSrc.push(getCspNonce)
+  // TODO: This is the SHA-256 hash of the inline script in build/reveal.js/plugins/notes/notes.html
+  // Any more clean solution appreciated.
+  directives.scriptSrc.push('\'sha256-EtvSSxRwce5cLeFBZbvZvDrTiRoyoXbWWwvEVciM5Ag=\'')
+}
+
+function getCspNonce (req, res) {
+  return "'nonce-" + res.locals.nonce + "'"
+}
+
+function addUpgradeUnsafeRequestsOptionTo (directives) {
+  if (config.csp.upgradeInsecureRequests === 'auto' && config.usessl) {
+    directives.upgradeInsecureRequests = true
+  } else if (config.csp.upgradeInsecureRequests === true) {
+    directives.upgradeInsecureRequests = true
+  }
+}
+
+CspStrategy.addNonceToLocals = function (req, res, next) {
+  res.locals.nonce = uuid.v4()
+  next()
+}
+
+module.exports = CspStrategy
diff --git a/lib/response.js b/lib/response.js
index 1c04f9f6..445aa0d7 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -598,7 +598,8 @@ function showPublishSlide (req, res, next) {
         lastchangeuserprofile: note.lastchangeuser ? models.User.getProfile(note.lastchangeuser) : null,
         robots: meta.robots || false, // default allow robots
         GA: meta.GA,
-        disqus: meta.disqus
+        disqus: meta.disqus,
+        cspNonce: res.locals.nonce
       }
       return renderPublishSlide(data, res)
     }).catch(function (err) {
diff --git a/package.json b/package.json
index bdb59635..885eee92 100644
--- a/package.json
+++ b/package.json
@@ -118,6 +118,7 @@
     "tedious": "^1.14.0",
     "to-markdown": "^3.0.3",
     "toobusy-js": "^0.5.1",
+    "uuid": "^3.1.0",
     "uws": "~0.14.1",
     "validator": "^6.2.0",
     "velocity-animate": "^1.4.0",
diff --git a/public/js/mathjax-config-extra.js b/public/js/mathjax-config-extra.js
new file mode 100644
index 00000000..11ba59c6
--- /dev/null
+++ b/public/js/mathjax-config-extra.js
@@ -0,0 +1,8 @@
+window.MathJax = {
+  messageStyle: 'none',
+  skipStartupTypeset: true,
+  tex2jax: {
+    inlineMath: [['$', '$'], ['\\(', '\\)']],
+    processEscapes: true
+  }
+}
diff --git a/public/views/hackmd/foot.ejs b/public/views/hackmd/foot.ejs
index 16ef5737..fc971132 100644
--- a/public/views/hackmd/foot.ejs
+++ b/public/views/hackmd/foot.ejs
@@ -1,6 +1,4 @@
-<script type="text/x-mathjax-config">
-    MathJax.Hub.Config({ messageStyle: "none", skipStartupTypeset: true ,tex2jax: {inlineMath: [['$','$'], ['\\(','\\)']], processEscapes: true }});
-</script>
+<script src="<%= url %>/js/mathjax-config-extra.js"></script>
 <% if(useCDN) { %>
 <script src="https://cdnjs.cloudflare.com/ajax/libs/spin.js/2.3.2/spin.min.js" integrity="sha256-PieqE0QdEDMppwXrTzSZQr6tWFX3W5KkyRVyF1zN3eg=" crossorigin="anonymous" defer></script>
 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js" integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8=" crossorigin="anonymous"></script>
diff --git a/public/views/pretty.ejs b/public/views/pretty.ejs
index db72fdc4..91d9c36c 100644
--- a/public/views/pretty.ejs
+++ b/public/views/pretty.ejs
@@ -72,9 +72,7 @@
 </body>
 
 </html>
-<script type="text/x-mathjax-config">
-    MathJax.Hub.Config({ messageStyle: "none", skipStartupTypeset: true ,tex2jax: {inlineMath: [['$','$'], ['\\(','\\)']], processEscapes: true }});
-</script>
+<script src="<%= url %>/js/mathjax-config-extra.js"></script>
 <% if(useCDN) { %>
 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js" integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8=" crossorigin="anonymous"></script>
 <script src="https://cdnjs.cloudflare.com/ajax/libs/velocity/1.4.0/velocity.min.js" integrity="sha256-bhm0lgEt6ITaZCDzZpkr/VXVrLa5RP4u9v2AYsbzSUk=" crossorigin="anonymous" defer></script>
diff --git a/public/views/slide.ejs b/public/views/slide.ejs
index 3572476f..942add4f 100644
--- a/public/views/slide.ejs
+++ b/public/views/slide.ejs
@@ -41,7 +41,7 @@
         <link rel="stylesheet" href="<%- url %>/css/slide.css">
 
         <!-- Printing and PDF exports -->
-        <script>
+        <script nonce="<%= cspNonce %>">
             var link = document.createElement( 'link' );
             link.rel = 'stylesheet';
             link.type = 'text/css';
@@ -89,9 +89,7 @@
             </div>
         </div>
 
-        <script type="text/x-mathjax-config">
-            MathJax.Hub.Config({ messageStyle: "none", skipStartupTypeset: true ,tex2jax: {inlineMath: [['$','$'], ['\\(','\\)']], processEscapes: true }});
-        </script>
+        <script src="<%= url %>/js/mathjax-config-extra.js"></script>
         <% if(useCDN) { %>
         <script src="https://cdnjs.cloudflare.com/ajax/libs/reveal.js/3.3.0/lib/js/head.min.js" integrity="sha256-+09kLhwACKXFPDvqo4xMMvi4+uXFsRZ2uYGbeN1U8sI=" crossorigin="anonymous"></script>
         <script src="https://cdnjs.cloudflare.com/ajax/libs/reveal.js/3.3.0/js/reveal.min.js" integrity="sha256-lvaInSKflJWLPqf5N5oHr/UZFwXKD6gckerdwoHqECY=" crossorigin="anonymous"></script>