Electron: Is it safe to expose ipcRenderer methods with only a startsWith if statement "protection"?

Question

I have an electron application and I'm using contextBridge.exposeInMainWorld to expose some ipcRenderer methods such as .on , .removeListener and .invoke, these methods are "protected" by having an if statement that checks if the "channel" passed is valid.

Using the following code:

const validateIPC = (channel) => {
  if (!channel || !channel.startsWith("myapp:")) 
    return false;
 
  return true;
};

contextBridge.exposeInMainWorld("electron", {
ipcRenderer: {
    on(channel, listener) {
      if (validateIPC(channel)) {
        ipcRenderer.on(channel, (evt, message) => {
          listener(evt, message);
        });
      }
    },
    removeListener(channel, listener) {
      if (validateIPC(channel)) {
        ipcRenderer.removeListener(channel, (evt, message) => {
          listener(evt, message);
        });
      }
    },
    invoke(channel, data) {
      if (validateIPC(channel)) {
        return ipcRenderer.invoke(channel, data);
      }
    },
  },
};

Is it safe to only check if the channel starts with some random string? I saw this on the source code of vscode available on github, however I also read some solutions using an array of strings to validate the channels. If it is safe why can't I just expose it without checking if the channel startsWith some random name? Are there any default channel that can't be exposed?

Answer 1

Yes, it is absolutely safe to check if your channel name only begins with a "certain" string. If it is a "random" string then one may argue that there is little reason to worry about even implementing a "channel naming" system.

You are correct in that you can just expose the ipcRenderer methods without using channel names. That in itself is not a security concern.

EG:

// Import the necessary Electron components.
const contextBridge = require('electron').contextBridge;
const ipcRenderer = require('electron').ipcRenderer;

// Exposed protected methods in the render process.
contextBridge.exposeInMainWorld("electron", {
    ipcRenderer: {
        on(channel, listener) {
            ipcRenderer.on(channel, (evt, message) => {
                listener(evt, message);
            });
        },
        removeListener(channel, listener) {
            ipcRenderer.removeListener(channel, (evt, message) => {
                listener(evt, message);
            });
        },
        invoke(channel, data) {
            return ipcRenderer.invoke(channel, data);
        }
    }
};

What is a security concern is if you set nodeIntegration: true and contextIsolation: false during the creation of your window. That would allow anyone who can run Javascript in your render (EG: If DevTools is still accessible) to access the main thread and possibly call all sorts of Node.js and user defined function. EG: Access to online databases or API's using any main thread hard-coded API key(s).

Another security concerns would be if you add particular electron API's to your preload.js script that just should not be accessible from the render thread(s) at all.

As to "default channels that can't be exposed", channels themselves are not an issue, it is any underlying (exposed) functions that may pose a security concern if accessible from the render thread(s).

Implementing a "Channel Naming" system within your preload.js file just allows for an easier way to track and manage IPC events, just like one does with Node.js events. It's not for everyone and in no way is it compulsory / required to have a preload.js script that used the “channel naming” system. It is purely personal preference.