Electron's Content-Secrity-Policy disabling eval not applied consistently in renderers with sandbox disabled

Impact

A Content-Security-Policy that disables eval, specifically setting a script-src directive and not providing unsafe-eval in that directive, is not respected in renderers that have sandbox and contextIsolation disabled. i.e. sandbox: false and contextIsolation: false in the webPreferences object.

This resulted in incorrectly allowing usage of methods like eval() and new Function, which can result in an expanded attack surface.

Patches

This issue only ever affected the 22 and 23 major versions of Electron and has been fixed in the latest versions of those release lines. Specifically, these versions contain the fixes:

• 22.0.1
• 23.0.0-alpha.2

We recommend all apps upgrade to the latest stable version of Electron, especially if they use sandbox: false or contextIsolation: false.

Workarounds

If upgrading isn’t possible, this issue can be addressed without upgrading by enabling at least one of sandbox: true or contextIsolation: true on all renderers.

const mainWindow = new BrowserWindow({
  webPreferences: {
    sandbox: true,
  }
});

For more information

If you have any questions or comments about this advisory, email us at [email protected].

Credit

Thanks to user @andreasdj for reporting this issue.