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?
The security concerns are often overblown. The bigger problem for me is I don’t know what kind of mess it’s going to make or whether I can undo it. If it’s a .deb or even a tarball to extract in /usr/local then I know how to uninstall.
I will still use them sometimes but for things I know and understand - e.g. rustup will put things in ~/.rustup and update the PATH in my shell profile and because I know that’s what it does I’m happy to use the automation on a new system.
What does curl even do? Unstraighten? Seems like any other command I’d blindly paste from an internet thread into a terminal window to try to get something on Linux to work.
cURL (pronounced curl) stands for client for URL. It transfers data from a url, which you can then do things with.
When I modded some subreddits I had an automod rule that would target curl-bash pipes in comments and posts, and remove them. I took a fair bit of heat over that, but I wasn’t backing down.
I had a lot of respect for Tteck and had a couple discussions with him about that and why I was doing that. I saw that eventually he put a notice up that pretty much said what I did about understanding what a script does, and how the URL you use can be pointed to something else entirely long after the commandline is posted.
I usually read it first.
Download it and then read it. Curl has a different user agent than web browsers.
Yeah I guess if they were being especially nefarious they could supply two different scripts based on user-agent. But I meant what you said anyways… :) I download and then read through the script. I know this is a common thing and people are wary of doing it, but has anyone ever heard of there being something disreputable in one of this scripts? I personally haven’t yet.
I’ve seen it many times. It usually takes the form of fake websites that are impersonating the real thing. It is easy to manipulate Google results. Also, there have been a few cases where a bad design and a typo result in data loss.
I think safer approach is to:
- Download the script first, review its contents, and then execute.
- Ensure the URL uses HTTPS to reduce the risk of man-in-the-middle attacks
Install scripts are bad in general. ideally use officially packaged software.
But then they’d have to lay some guy 15$ to package it and thats like, spending money
Distros do the packaging. Devs can not be trusted
If you’ve downloaded and audited the script, there’s no reason to pipe it from curl to sh, just run it. No https necessary.
The https is to cover the factthat you might have missed something.
I guess I download and skim out of principle, but they might have hidden something in there.
Wat. All https does is encrypt the connection when downloading. If you’ve already downloaded the file to audit it, then it’s in your drive, no need to use curl to download it again and then pipe it to sh. Just click the thing.
Unpopular opinion, these are handy for quickly installing in a new vm or container (usually throwaway) where one don’t have to think much unless the script breaks. People don’t install thing on host or production multiple times, so anything installed there is usually vetted and most of the times from trusted sources like distro repos.
For normal threat model, it is not much different from downloading compiled binary from somewhere other than well trusted repos. Windows software ecosystem is famously infamous for exactly the same but it sticks around still.
Just use a VM or container for installing software. It can go horribly wrong in a isolated place.
You have the option of piping it into a file instead, inspecting that file for yourself and then running it, or running it in some sandboxed environment. Ultimately though, if you are downloading software over the internet you have to place a certain amount of trust in the person your downloading the software from. Even if you’re absolutely sure that the download script doesn’t wipe your home directory, you’re going to have to run the program at some point and it could just as easily wipe your home directory at that point instead.
Indeed, looking at the content of the script before running it is what I do if there is no alternative. But some of these scripts are awfully complex, and manually parsing the odd bash stuff is a pain, when all I want to know is : 1) what URL are you downloading stuff from? 2) where are you going to install the stuff?
As for running the program, I would trust it more than a random deployment script. People usually place more emphasis on testing the former, not so much the latter.
All the software I have is downloaded from the internet…
It is kind of cool, when you’ve actually written your own software and use that. But realistically, I’m still getting the compiler from the internet…
You should try downloading the software from your mind brain, like us elite hackers do it. Just dump the binary from memory into a txt file and exe that shit, playa!
You should start getting it from CD-roms, that shit you can trust
I got my software from these free USB sticks I found in the parking lot.
Ah, you’re one of my users
You have the option of piping it into a file instead, inspecting that file for yourself and then running it, or running it in some sandboxed environment.
That’s not what projects recommend though. Many recommend piping the output of an HTTP transfer over the public Internet directly into a shell interpreter. Even just
curl https://... > install.sh; sh install.shwould be one step up. The absolute minimum recommendation IMHO should be
curl https://... > install.sh; less install.sh; sh install.shbut this is still problematic.
Ultimately, installing software is a labourious process which requires care, attention and the informed use of GPG. It shouldn’t be simplified for convenience.
Also, FYI, the word “option” implies that I’m somehow restricted to a limited set of options in how I can use my GNU/Linux computer which is not the case.
Showing people that are running curl piped to bash the script they are about to run doesn’t really accomplish anything. If they can read bash and want to review the script then they can by just opening the URL, and the people that aren’t doing that don’t care what’s in the script, so why waste their time with it?
Do you think most users installing software from the AUR are actually reading the pkgbuilds? I’d guess it’s a pretty small percentage that do.
I mean if you think that it’s bad for linux culture because you’re teaching newbies the wrong lessons, fair enough.
My point is that most people can parse that they’re essentially asking you to run some commands at a url, and if you have even a fairly basic grasp of linux it’s easy to do that in whatever way you want. I don’t know if I personally would be any happier if people took the time to lecture me on safety habits, because I can interpret the command for myself.
curl https://some-url/ | shis terse and to the point, and I know not to take it completely literally.linux culture
snigger
you’re teaching newbies the wrong lessons
The problem is not that it’s teaching bad lessons, it’s that it’s actually doing bad things.
most people can parse that they’re essentially asking you to run some commands at a url
I know not to take it completely literally
Then it needn’t be written literally.
I think you’re giving the authors of such installation instructions too much credit. I think they intend people to take it literally. I think this because I’ve argued with many of them.
Who the fuck types out “snigger” haha
Teleports behind you
deleted by creator
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.
it is detectable on server side, if you download the script or pipe it into a shell
Irrelevant. This is just an excuse people use to try and win the argument after it is pointed out to them that there’s actually no security issue with
curl | bash.It’s waaaay easier to hide malicious code in a binary than it is in a Bash script.
You can still see the “hidden” shell script that is served for Bash - just pipe it through
teeand then into Bash.Can anyone even find one single instance of that trick ever actually being used in the wild (not as a demo)?
I never tried to win any argument. Hell I was not even aware that I’m participating in one. I just wanted to share the info, that even if the vendor is absolutely trustworthy and even if you validated the script by downloading and looking at it, there’s still another hole that’s not obvious to see.
Yes it’s unlikely, but again, I never said it were. There are also arguments you can run curl with, to tell it to do the download first and then push it through the pipe afterwards, though I don’t know them by heart now.
It won’t cost you anything to set those parameters, when you insist to use curl | bash, just in the off chance that someone’s trying to do what I mentioned.
But I’m also someone who usually validates their downloads with a checksum so maybe I’m just weird. Who knows.
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?
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:
You can also find some proof-of-concept implementations online to try it out yourself.
Wow, thanks for this. That is very helpful context. And thanks for your original post too, or I’d never have asked.
Oh, you’re welcome, kind person :)
It’s not much different from downloading and compiling source code, in terms of risk. A typo in the code could easily wipe home or something like that.
Obviously the package manager repo for your distro is the best option because there’s another layer of checking (in theory), but very often things aren’t in the repos.
The solution really is just backups and snapshots, there are a million ways to lose files or corrupt them.
You should use officially packaged software. That’s the safest option.
Those just don’t get installed. I refuse to install stuff that way. It’s to reminiscent of installing stuff on windows. “Pssst, hey bud, want to run this totally safe executable on your PC? It won’t do anything bad. Pinky promise”. Ain’t happening.
The only exception I make is for nix on non-nixos machines because thwt bootstraps everything and I’ve read that script a few times.
curl | sudo bash Gang
This is simpler than the download, ./configure, make, make install steps we had some decades ago, but not all that different in that you wind up with arbitrary, unmanaged stuff.
Preferably use the distro native packages, or else their build system if it’s easily available (e.g. AUR in Arch)
Saved that, thank you.
I usually just take a look at the code with a get request. Then if it looks good, then run manually. Most of the time, it’s fine. Sometimes there’s something that would break something on the system.
I haven’t seen anything explicitly nefarious, but it’s better to be safe than sorry.
