Requests to open external protocol URLs from web content did not take iframe sandbox restrictions into account, so a sandboxed iframe could cause an OS-registered external application to be launched. The frame's sandbox state was also not made available to the app's permission handlers.

Apps are only affected if they render untrusted content in sandboxed iframes and grant the openExternal permission (granted by default when no setPermissionRequestHandler is installed). Apps whose permission handler denies openExternal for untrusted content are not affected.

Install a setPermissionRequestHandler that denies the openExternal permission for untrusted content.

If you have any questions or comments about this advisory, email Electron at security@electronjs.org