undefined | Better HN

0 pointsseandougall6y ago0 comments

On macOS, if my understanding of the current situation is correct, code signing normally covers all binaries in an application bundle, including binaries in all bundled frameworks. What's different about Electron is that it puts application code, which is not a binary, into the Resources/ directory, which is not signed.

I just tried this out with Slack on macOS, and it did work... almost as advertised. I had to use sudo to change the application files, which means this isn't really much of a novel attack surface, but it did bypass the code signing checks quite handily.

So, is this a "vulnerability"? That may be a stretch, as far as I can see, but putting application code in Resources/ definitely counts as a "smell" in my book.

0 comments

marshallofsound6y ago

Hi, Electron maintainer here.

> I just tried this out with Slack on macOS, and it did work

Here's the thing with how gatekeeper works, that application had already passed gatekeeper and will never be _fully_ validated ever again.

If you zipped your modified Slack.app up, uploaded it to google drive, and downloaded it again. Gatekeeper would 100% reject that application, the ASAR file is included as part of the application signature. You can prove this by checking the "CodeResources" file in the apps signature.

You can't re-distribute the app without gatekeeper completely shutting you down.

seandougallOP6y ago

Thanks for taking the time to reply! Like many here, I've been a critic of Electron, but I think it also does some amazing stuff, and I'm sorry you have to go into PR maintenance mode over such a weaksauce article.

I was coming back to follow up and say that that's exactly what I found -- running `codesign --verify` does show the modification. It makes sense that Gatekeeper wouldn't re-verify a 185 MB bundle on every launch, which makes me wonder if there's something else macOS could be doing at the FS level to see if any files have been modified and trigger a new check.

At any rate, while I don't quite take back what I said about application code in Resources/, I do take back the implication that it had anything to do with this; I suppose there doesn't seem to be anything Electron-specific about TFA, other than that exposing raw JS lowers the bar for who can write the code to inject. (Assuming you can get FS access to inject code in the first place, of course.)

j / k navigate · click thread line to collapse