electron/lib/renderer/security-warnings.ts

import { webFrame } from 'electron';
import { ipcRendererInternal } from '@electron/internal/renderer/ipc-renderer-internal';
import { IPC_MESSAGES } from '@electron/internal/common/ipc-messages';

let shouldLog: boolean | null = null;

const { platform, execPath, env } = process;

/**
 * This method checks if a security message should be logged.
 * It does so by determining whether we're running as Electron,
 * which indicates that a developer is currently looking at the
 * app.
 *
 * @returns {boolean} - Should we log?
 */
const shouldLogSecurityWarnings = function (): boolean {
  if (shouldLog !== null) {
    return shouldLog;
  }

  switch (platform) {
    case 'darwin':
      shouldLog = execPath.endsWith('MacOS/Electron') ||
                  execPath.includes('Electron.app/Contents/Frameworks/');
      break;
    case 'freebsd':
    case 'linux':
      shouldLog = execPath.endsWith('/electron');
      break;
    case 'win32':
      shouldLog = execPath.endsWith('\\electron.exe');
      break;
    default:
      shouldLog = false;
  }

  if ((env && env.ELECTRON_DISABLE_SECURITY_WARNINGS) ||
      (window && window.ELECTRON_DISABLE_SECURITY_WARNINGS)) {
    shouldLog = false;
  }

  if ((env && env.ELECTRON_ENABLE_SECURITY_WARNINGS) ||
      (window && window.ELECTRON_ENABLE_SECURITY_WARNINGS)) {
    shouldLog = true;
  }

  return shouldLog;
};

/**
 * Checks if the current window is remote.
 *
 * @returns {boolean} - Is this a remote protocol?
 */
const getIsRemoteProtocol = function () {
  if (window && window.location && window.location.protocol) {
    return /^(http|ftp)s?/gi.test(window.location.protocol);
  }
};

/**
 * Checks if the current window is from localhost.
 *
 * @returns {boolean} - Is current window from localhost?
 */
const isLocalhost = function () {
  if (!window || !window.location) {
    return false;
  }

  return window.location.hostname === 'localhost';
};

/**
 * Tries to determine whether a CSP without `unsafe-eval` is set.
 *
 * @returns {boolean} Is a CSP with `unsafe-eval` set?
 */
const isUnsafeEvalEnabled: () => Promise<boolean> = function () {
  // Call _executeJavaScript to bypass the world-safe deprecation warning
  return webFrame._executeJavaScript(`(${(() => {
    try {
      eval(window.trustedTypes.emptyScript); // eslint-disable-line no-eval
    } catch {
      return false;
    }
    return true;
  }).toString()})()`, false);
};

const moreInformation = `\nFor more information and help, consult
https://electronjs.org/docs/tutorial/security.\nThis warning will not show up
once the app is packaged.`;

/**
 * #1 Only load secure content
 *
 * Checks the loaded resources on the current page and logs a
 * message about all resources loaded over HTTP or FTP.
 */
const warnAboutInsecureResources = function () {
  if (!window || !window.performance || !window.performance.getEntriesByType) {
    return;
  }

  const isLocal = (url: URL): boolean =>
    ['localhost', '127.0.0.1', '[::1]', ''].includes(url.hostname);
  const isInsecure = (url: URL): boolean =>
    ['http:', 'ftp:'].includes(url.protocol) && !isLocal(url);

  const resources = window.performance
    .getEntriesByType('resource')
    .filter(({ name }) => isInsecure(new URL(name)))
    .map(({ name }) => `- ${name}`)
    .join('\n');

  if (!resources || resources.length === 0) {
    return;
  }

  const warning = `This renderer process loads resources using insecure
  protocols. This exposes users of this app to unnecessary security risks.
  Consider loading the following resources over HTTPS or FTPS. \n${resources}
  \n${moreInformation}`;

  console.warn('%cElectron Security Warning (Insecure Resources)',
    'font-weight: bold;', warning);
};

/**
 * #2 on the checklist: Disable the Node.js integration in all renderers that
 * display remote content
 *
 * Logs a warning message about Node integration.
 */
const warnAboutNodeWithRemoteContent = function (nodeIntegration: boolean) {
  if (!nodeIntegration || isLocalhost()) return;

  if (getIsRemoteProtocol()) {
    const warning = `This renderer process has Node.js integration enabled
    and attempted to load remote content from '${window.location}'. This
    exposes users of this app to severe security risks.\n${moreInformation}`;

    console.warn('%cElectron Security Warning (Node.js Integration with Remote Content)',
      'font-weight: bold;', warning);
  }
};

// Currently missing since it has ramifications and is still experimental:
//   #3 Enable context isolation in all renderers that display remote content
//
// Currently missing since we can't easily programmatically check for those cases:
//   #4 Use ses.setPermissionRequestHandler() in all sessions that load remote content

/**
 * #5 on the checklist: Do not disable websecurity
 *
 * Logs a warning message about disabled webSecurity.
 */
const warnAboutDisabledWebSecurity = function (webPreferences?: Electron.WebPreferences) {
  if (!webPreferences || webPreferences.webSecurity !== false) return;

  const warning = `This renderer process has "webSecurity" disabled. This
  exposes users of this app to severe security risks.\n${moreInformation}`;

  console.warn('%cElectron Security Warning (Disabled webSecurity)',
    'font-weight: bold;', warning);
};

/**
 * #6 on the checklist: Define a Content-Security-Policy and use restrictive
 * rules (i.e. script-src 'self')
 *
 * Logs a warning message about unset or insecure CSP
 */
const warnAboutInsecureCSP = function () {
  isUnsafeEvalEnabled().then((enabled) => {
    if (!enabled) return;

    const warning = `This renderer process has either no Content Security
    Policy set or a policy with "unsafe-eval" enabled. This exposes users of
    this app to unnecessary security risks.\n${moreInformation}`;

    console.warn('%cElectron Security Warning (Insecure Content-Security-Policy)',
      'font-weight: bold;', warning);
  }).catch(() => {});
};

/**
 * #7 on the checklist: Do not set allowRunningInsecureContent to true
 *
 * Logs a warning message about disabled webSecurity.
 */
const warnAboutInsecureContentAllowed = function (webPreferences?: Electron.WebPreferences) {
  if (!webPreferences || !webPreferences.allowRunningInsecureContent) return;

  const warning = `This renderer process has "allowRunningInsecureContent"
  enabled. This exposes users of this app to severe security risks.\n
  ${moreInformation}`;

  console.warn('%cElectron Security Warning (allowRunningInsecureContent)',
    'font-weight: bold;', warning);
};

/**
 * #8 on the checklist: Do not enable experimental features
 *
 * Logs a warning message about experimental features.
 */
const warnAboutExperimentalFeatures = function (webPreferences?: Electron.WebPreferences) {
  if (!webPreferences || (!webPreferences.experimentalFeatures)) {
    return;
  }

  const warning = `This renderer process has "experimentalFeatures" enabled.
  This exposes users of this app to some security risk. If you do not need
  this feature, you should disable it.\n${moreInformation}`;

  console.warn('%cElectron Security Warning (experimentalFeatures)',
    'font-weight: bold;', warning);
};

/**
 * #9 on the checklist: Do not use enableBlinkFeatures
 *
 * Logs a warning message about enableBlinkFeatures
 */
const warnAboutEnableBlinkFeatures = function (webPreferences?: Electron.WebPreferences) {
  if (!webPreferences ||
    !Object.prototype.hasOwnProperty.call(webPreferences, 'enableBlinkFeatures') ||
    (webPreferences.enableBlinkFeatures != null && webPreferences.enableBlinkFeatures.length === 0)) {
    return;
  }

  const warning = `This renderer process has additional "enableBlinkFeatures"
  enabled. This exposes users of this app to some security risk. If you do not
  need this feature, you should disable it.\n${moreInformation}`;

  console.warn('%cElectron Security Warning (enableBlinkFeatures)',
    'font-weight: bold;', warning);
};

/**
 * #10 on the checklist: Do Not Use allowpopups
 *
 * Logs a warning message about allowed popups
 */
const warnAboutAllowedPopups = function () {
  if (document && document.querySelectorAll) {
    const domElements = document.querySelectorAll('[allowpopups]');

    if (!domElements || domElements.length === 0) {
      return;
    }

    const warning = `A <webview> has "allowpopups" set to true. This exposes
    users of this app to some security risk, since popups are just
    BrowserWindows. If you do not need this feature, you should disable it.\n
    ${moreInformation}`;

    console.warn('%cElectron Security Warning (allowpopups)',
      'font-weight: bold;', warning);
  }
};

// Currently missing since we can't easily programmatically check for it:
//   #11 Verify WebView Options Before Creation
//   #12 Disable or limit navigation
//   #13 Disable or limit creation of new windows
//   #14 Do not use `openExternal` with untrusted content

// #15 on the checklist: Disable the `remote` module
// Logs a warning message about the remote module

const warnAboutRemoteModuleWithRemoteContent = function (webPreferences?: Electron.WebPreferences) {
  if (!webPreferences || !webPreferences.enableRemoteModule || isLocalhost()) return;

  if (getIsRemoteProtocol()) {
    const warning = `This renderer process has "enableRemoteModule" enabled
    and attempted to load remote content from '${window.location}'. This
    exposes users of this app to unnecessary security risks.\n${moreInformation}`;

    console.warn('%cElectron Security Warning (enableRemoteModule)',
      'font-weight: bold;', warning);
  }
};

// Currently missing since we can't easily programmatically check for it:
//   #16 Filter the `remote` module

const logSecurityWarnings = function (
  webPreferences: Electron.WebPreferences | undefined, nodeIntegration: boolean
) {
  warnAboutNodeWithRemoteContent(nodeIntegration);
  warnAboutDisabledWebSecurity(webPreferences);
  warnAboutInsecureResources();
  warnAboutInsecureContentAllowed(webPreferences);
  warnAboutExperimentalFeatures(webPreferences);
  warnAboutEnableBlinkFeatures(webPreferences);
  warnAboutInsecureCSP();
  warnAboutAllowedPopups();
  if (BUILDFLAG(ENABLE_REMOTE_MODULE)) {
    warnAboutRemoteModuleWithRemoteContent(webPreferences);
  }
};

const getWebPreferences = async function () {
  try {
    return ipcRendererInternal.invoke<Electron.WebPreferences>(IPC_MESSAGES.BROWSER_GET_LAST_WEB_PREFERENCES);
  } catch (error) {
    console.warn(`getLastWebPreferences() failed: ${error}`);
  }
};

export function securityWarnings (nodeIntegration: boolean) {
  const loadHandler = async function () {
    if (shouldLogSecurityWarnings()) {
      const webPreferences = await getWebPreferences();
      logSecurityWarnings(webPreferences, nodeIntegration);
    }
  };
  window.addEventListener('load', loadHandler, { once: true });
}