electron/lib/renderer/security-warnings.js

let shouldLog = null

/**
 * 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 () {
  if (shouldLog !== null) {
    return shouldLog
  }

  const { platform, execPath, env } = process

  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)
  }
}

/**
 * Tries to determine whether a CSP without `unsafe-eval` is set.
 *
 * @returns {boolean} Is a CSP with `unsafe-eval` set?
 */
const isUnsafeEvalEnabled = function () {
  const { webFrame } = require('electron')

  return new Promise((resolve) => {
    webFrame.executeJavaScript(`(${(() => {
      try {
        new Function('') // eslint-disable-line no-new,no-new-func
      } catch (err) {
        return false
      }
      return true
    }).toString()})()`, resolve)
  })
}

/**
 * Attempts to get the current webContents. Returns null
 * if that fails
 *
 * @returns {Object|null} webPreferences
 */
let webPreferences
const getWebPreferences = function () {
  try {
    if (webPreferences) {
      return webPreferences
    }

    const { remote } = require('electron')
    webPreferences = remote.getCurrentWebContents().getLastWebPreferences()
    return webPreferences
  } catch (error) {
    return null
  }
}

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

module.exports = {
  shouldLogSecurityWarnings,

  /**
   * #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.
   */
  warnAboutInsecureResources: () => {
    if (!window || !window.performance || !window.performance.getEntriesByType) {
      return
    }

    const resources = window.performance
      .getEntriesByType('resource')
      .filter(({ name }) => /^(http|ftp):/gi.test(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.
   */
  warnAboutNodeWithRemoteContent: () => {
    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.
   */
  warnAboutDisabledWebSecurity: () => {
    const webPreferences = getWebPreferences()
    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')
   *
   * #7 on the checklist: Disable eval
   *
   * Logs a warning message about unset or insecure CSP
   */
  warnAboutInsecureCSP: () => {
    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)
    })
  },

  /**
   * #8 on the checklist: Do not set allowRunningInsecureContent to true
   *
   * Logs a warning message about disabled webSecurity.
   */
  warnAboutInsecureContentAllowed: () => {
    const webPreferences = getWebPreferences()
    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)
  },

  /**
   * #9 on the checklist: Do not enable experimental features
   *
   * Logs a warning message about experimental features.
   */
  warnAboutExperimentalFeatures: () => {
    const webPreferences = getWebPreferences()
    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)
  },

  /**
   * #10 on the checklist: Do not use enableBlinkFeatures
   *
   * Logs a warning message about enableBlinkFeatures
   */
  warnAboutEnableBlinkFeatures: () => {
    const webPreferences = getWebPreferences()
    if (webPreferences === null ||
      !webPreferences.hasOwnProperty('enableBlinkFeatures') ||
      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)
  },

  /**
   * #11 on the checklist: Do Not Use allowpopups
   *
   * Logs a warning message about allowed popups
   */
  warnAboutAllowedPopups: () => {
    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:
  //   #12WebViews: Verify the options and params of all `<webview>` tags
}