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Am in the only one who cringes at install instructions that require piping some curl output into bash? (programming.dev)

submitted 2 days ago by cschreib@programming.dev to c/linux@programming.dev

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curl https://some-url | sh

I see this all over the place nowadays, even in communities that, I would think, should be security conscious. How is that safe? What's stopping the downloaded script from wiping my home directory? If you use this, how can you feel comfortable?

I understand that we have the same problems with the installed application, even if it was downloaded and installed manually. But I feel the bar for making a mistake in a shell script is much lower than in whatever language the main application is written. Don't we have something better than "sh" for this? Something with less power to do harm?

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[-] Undaunted@feddit.org 21 points 1 day ago

You shouldn't install software from someone you don't trust anyway because even if the installation process is save, the software itself can do whatever it has permission to.

"So if you trust their software, why not their install script?" you might ask. Well, it is detectable on server side, if you download the script or pipe it into a shell. So even if the vendor it trustworthy, there could be a malicious middle man, that gives you the original and harmless script, when you download it, and serves you a malicious one when you pipe it into your shell.

And I think this is not obvious and very scary.

[-] August27th@lemmy.ca 8 points 1 day ago

it is detectable [...] server side, if you download the script [vs] pipe it into a shell

I presume you mean if you download the script in a browser, vs using curl to retrieve it, where presumably you are piping it to a shell. Because yeah, the user agent is going to reveal which tool downloaded it, of course. You can use curl to simply retrieve the file without executing it though.

Or are you suggesting that curl makes something different in its request to the server for the file, depending on whether it is saving the file to disk vs streaming it to a pipe?

[-] Undaunted@feddit.org 12 points 1 day ago

It is actually a passive detection based of the timing of the chunk requests. Because curl by default will only request new chunks when the buffer is freed by the shell executing the given commands. This then can be used to detect that someone is not merely downloading but simultaneously executing it. Here's a writeup about it:

https://web.archive.org/web/20250209133823/https://www.idontplaydarts.com/2016/04/detecting-curl-pipe-bash-server-side/

You can also find some proof-of-concept implementations online to try it out yourself.