Introduce content security policy (CSP) (#29545) (#30686)

* csp: nonce and unsafe-eval for scripts

To kick things off, a rudimentary CSP implementation only allows
dynamically loading new JavaScript if it includes an associated nonce
that is generated on every load of the app.

A more sophisticated content security policy is necessary, particularly
one that bans eval for scripts, but one step at a time.

* img-src is not necessary if the goal is not to restrict

* configurable CSP owned by security team

* smoke test

* remove x-content-security-policy

* document csp.rules

* fix tsconfig for test

* switch integration test back to regular js

* stop looking for tsconfig in test

* grrr, linting errors not caught by precommit

* docs: people -> you for consistency sake

Co-Authored-By: epixa <court@epixa.com>

docs/setup/settings.asciidoc

@@ -19,6 +19,8 @@ you'll need to update your `kibana.yml` file. You can also enable SSL and set a
 
 `cpuacct.cgroup.path.override:`:: Override for cgroup cpuacct path when mounted in manner that is inconsistent with `/proc/self/cgroup`
 
+`csp.rules:`:: A template https://w3c.github.io/webappsec-csp/[content-security-policy] that disables certain unnecessary and potentially insecure capabilities in the browser. All instances of `{nonce}` will be replaced with an automatically generated nonce at load time. We strongly recommend that you keep the default CSP rules that ship with Kibana.
+
 `elasticsearch.customHeaders:`:: *Default: `{}`* Header names and values to send to Elasticsearch. Any custom headers
 cannot be overwritten by client-side headers, regardless of the `elasticsearch.requestHeadersWhitelist` configuration.
 

packages/kbn-interpreter/package.json

@@ -11,7 +11,6 @@
   "dependencies": {
     "lodash": "npm:@elastic/lodash@3.10.1-kibana1",
     "lodash.clone": "^4.5.0",
-    "scriptjs": "^2.5.8",
     "uuid": "3.0.1"
   },
   "devDependencies": {
@@ -22,8 +21,8 @@
     "babel-loader": "7.1.5",
     "babel-plugin-transform-runtime": "^6.23.0",
     "babel-polyfill": "6.20.0",
-    "css-loader": "1.0.0",
     "copy-webpack-plugin": "^4.6.0",
+    "css-loader": "1.0.0",
     "del": "^3.0.0",
     "getopts": "^2.2.3",
     "pegjs": "0.9.0",

packages/kbn-interpreter/src/public/browser_registries.js

@@ -17,7 +17,19 @@
  * under the License.
  */
 
-import $script from 'scriptjs';
+function loadPath(path, callback) {
+  const script = document.createElement('script');
+
+  script.setAttribute('async', '');
+  script.setAttribute('nonce', window.__webpack_nonce__);
+  script.addEventListener('error', () => {
+    console.error('Failed to load plugin bundle', path);
+  });
+  script.setAttribute('src', path);
+  script.addEventListener('load', callback);
+
+  document.head.appendChild(script);
+}
 
 export const loadBrowserRegistries = (registries, basePath) => {
   const remainingTypes = Object.keys(registries);
@@ -36,7 +48,7 @@ export const loadBrowserRegistries = (registries, basePath) => {
       // Load plugins one at a time because each needs a different loader function
       // $script will only load each of these once, we so can call this as many times as we need?
       const pluginPath = `${basePath}/api/canvas/plugins?type=${type}`;
-      $script(pluginPath, () => {
+      loadPath(pluginPath, () => {
         populatedTypes[type] = registries[type];
         loadType();
       });

src/server/config/schema.js

@@ -21,8 +21,13 @@ import Joi from 'joi';
 import { constants as cryptoConstants } from 'crypto';
 import os from 'os';
 
-import { fromRoot } from '../../utils';
-import { getData } from '../path';
+import {
+  fromRoot
+} from '../../utils';
+import {
+  getData
+} from '../path';
+import { DEFAULT_CSP_RULES } from '../csp';
 
 const tilemapSchema = Joi.object({
   url: Joi.string(),
@@ -88,6 +93,10 @@ export default () => Joi.object({
     exclusive: Joi.boolean().default(false)
   }).default(),
 
+  csp: Joi.object({
+    rules: Joi.array().items(Joi.string()).default(DEFAULT_CSP_RULES),
+  }).default(),
+
   cpu: Joi.object({
     cgroup: Joi.object({
       path: Joi.object({

src/server/csp/index.test.ts

@@ -0,0 +1,72 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { createCSPRuleString, DEFAULT_CSP_RULES, generateCSPNonce } from './';
+
+// CSP rules aren't strictly additive, so any change can potentially expand or
+// restrict the policy in a way we consider a breaking change. For that reason,
+// we test the default rules exactly so any change to those rules gets flagged
+// for manual review. In otherwords, this test is intentionally fragile to draw
+// extra attention if defaults are modified in any way.
+//
+// A test failure here does not necessarily mean this change cannot be made,
+// but any change here should undergo sufficient scrutiny by the Kibana
+// security team.
+//
+// The tests use inline snapshots to make it as easy as possible to identify
+// the nature of a change in defaults during a PR review.
+test('default CSP rules', () => {
+  expect(DEFAULT_CSP_RULES).toMatchInlineSnapshot(`
+Array [
+  "script-src 'unsafe-eval' 'nonce-{nonce}'",
+  "worker-src blob:",
+  "child-src blob:",
+]
+`);
+});
+
+test('generateCSPNonce() creates a 16 character string', async () => {
+  const nonce = await generateCSPNonce();
+
+  expect(nonce).toHaveLength(16);
+});
+
+test('generateCSPNonce() creates a new string on each call', async () => {
+  const nonce1 = await generateCSPNonce();
+  const nonce2 = await generateCSPNonce();
+
+  expect(nonce1).not.toEqual(nonce2);
+});
+
+test('createCSPRuleString() converts an array of rules into a CSP header string', () => {
+  const csp = createCSPRuleString([`string-src 'self'`, 'worker-src blob:', 'img-src data: blob:']);
+
+  expect(csp).toMatchInlineSnapshot(`"string-src 'self'; worker-src blob:; img-src data: blob:"`);
+});
+
+test('createCSPRuleString() replaces all occurrences of {nonce} if provided', () => {
+  const csp = createCSPRuleString(
+    [`string-src 'self' 'nonce-{nonce}'`, 'img-src data: blob:', `default-src  'nonce-{nonce}'`],
+    'foo'
+  );
+
+  expect(csp).toMatchInlineSnapshot(
+    `"string-src 'self' 'nonce-foo'; img-src data: blob:; default-src  'nonce-foo'"`
+  );
+});

src/server/csp/index.ts

@@ -0,0 +1,41 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { randomBytes } from 'crypto';
+import { promisify } from 'util';
+
+const randomBytesAsync = promisify(randomBytes);
+
+export const DEFAULT_CSP_RULES = Object.freeze([
+  `script-src 'unsafe-eval' 'nonce-{nonce}'`,
+  'worker-src blob:',
+  'child-src blob:',
+]);
+
+export async function generateCSPNonce() {
+  return (await randomBytesAsync(12)).toString('base64');
+}
+
+export function createCSPRuleString(rules: string[], nonce?: string) {
+  let ruleString = rules.join('; ');
+  if (nonce) {
+    ruleString = ruleString.replace(/\{nonce\}/g, nonce);
+  }
+  return ruleString;
+}

src/ui/ui_render/bootstrap/template.js.hbs

@@ -50,6 +50,7 @@ window.onload = function () {
     var dom = document.createElement('script');
 
     dom.setAttribute('async', '');
+    dom.setAttribute('nonce', window.__webpack_nonce__);
     dom.addEventListener('error', failure);
     dom.setAttribute('src', file);
     dom.addEventListener('load', next);

src/ui/ui_render/ui_render_mixin.js

@@ -25,6 +25,7 @@ import { i18n } from '@kbn/i18n';
 import { AppBootstrap } from './bootstrap';
 import { mergeVariables } from './lib';
 import { fromRoot } from '../../utils';
+import { generateCSPNonce, createCSPRuleString } from '../../server/csp';
 
 export function uiRenderMixin(kbnServer, server, config) {
   function replaceInjectedVars(request, injectedVars) {
@@ -176,7 +177,10 @@ export function uiRenderMixin(kbnServer, server, config) {
     const request = h.request;
     const basePath = request.getBasePath();
 
-    return h.view('ui_app', {
+    const nonce = await generateCSPNonce();
+
+    const response = h.view('ui_app', {
+      nonce,
       uiPublicUrl: `${basePath}/ui`,
       bootstrapScriptUrl: `${basePath}/bundles/app/${app.getId()}/bootstrap.js`,
       i18n: (id, options) => i18n.translate(id, options),
@@ -206,6 +210,11 @@ export function uiRenderMixin(kbnServer, server, config) {
         }),
       },
     });
+
+    const csp = createCSPRuleString(config.get('csp.rules'), nonce);
+    response.header('content-security-policy', csp);
+
+    return response;
   }
 
   server.decorate('toolkit', 'renderApp', function (app, injectedVarsOverrides) {

src/ui/ui_render/views/ui_app.pug

@@ -110,4 +110,6 @@ block content
     .kibanaWelcomeText(data-error-message=i18n('common.ui.welcomeErrorMessage', { defaultMessage: 'Kibana did not load properly. Check the server output for more information.' }))
       | #{i18n('common.ui.welcomeMessage', { defaultMessage: 'Loading Kibana' })}
 
-  script(src=bootstrapScriptUrl)
+  script(nonce=nonce).
+    window.__webpack_nonce__ = '!{nonce}';
+  script(src=bootstrapScriptUrl, nonce=nonce)

test/api_integration/apis/general/csp.js

@@ -0,0 +1,39 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import expect from 'expect.js';
+
+export default function ({ getService }) {
+  const supertest = getService('supertest');
+
+  describe('csp smoke test', () => {
+    it('app response sends content security policy headers', async () => {
+      const response = await supertest.get('/app/kibana');
+
+      expect(response.headers).to.have.property('content-security-policy');
+    });
+
+    it('csp header does not allow all inline scripts', async () => {
+      const response = await supertest.get('/app/kibana');
+
+      expect(response.headers['content-security-policy']).to.contain('script-src');
+      expect(response.headers['content-security-policy']).not.to.contain('unsafe-inline');
+    });
+  });
+}

test/api_integration/apis/general/index.js

@@ -20,5 +20,6 @@
 export default function ({ loadTestFile }) {
   describe('general', () => {
     loadTestFile(require.resolve('./cookies'));
+    loadTestFile(require.resolve('./csp'));
   });
 }

yarn.lock

@@ -19222,11 +19222,6 @@ script-loader@0.7.2:
   dependencies:
     raw-loader "~0.5.1"
 
-scriptjs@^2.5.8:
-  version "2.5.8"
-  resolved "https://registry.yarnpkg.com/scriptjs/-/scriptjs-2.5.8.tgz#d0c43955c2e6bad33b6e4edf7b53b8965aa7ca5f"
-  integrity sha1-0MQ5VcLmutM7bk7fe1O4llqnyl8=
-
 scroll-into-view@^1.3.0:
   version "1.9.1"
   resolved "https://registry.yarnpkg.com/scroll-into-view/-/scroll-into-view-1.9.1.tgz#90c3b338422f9fddaebad90e6954790940dc9c1e"