There is no legitimate reason why postinstall scripts need to exist. The npm team needs to grow up and declare "starting with npm version whatever, npm will only run postinstall scripts for versions of packages published before ${today}".
I audited several postinstall scripts recently in popular packages. They seem to be mostly around using native binaries, downloading them, detecting if the platform is compatible, linking to it directly instead of having it bootstrapped by node, working around issues in older versions of npm, etc. Since dev toolchains (e.g. esbuild) are now being built in compiled languages and distributed as binaries via npm registry. If you are on a recent version of node/npm and a common/recent OS/platform, you should be able to disable all the postinstall scripts without legitimate issue.
With respect, post-install scripts are a total red herring. You're alarmed by them because they are code controlled by someone else that runs on your box, and they could do something bad -- yes, they are, and yes they could.
But so is the regular code in those packages! It won't run at install time, but something in there will run -- otherwise it wouldn't have been included in the dependencies.
Thinking that eliminating post-install scripts will have more than a momentary impact on exploitation rates is a sign of not thinking the issue through. Unfortunately the issue is much more nuanced than TFA implies -- it's not at all a case of "Let's just stop putting the wings-fall-off button next to the light switch", it's that the thing we want to prevent (other people's bad code running on our box) cannot be distinguished from the thing we want (other people's good code running on our box) without a whole lot of painstaking manual effort, and avoiding painstaking manual effort is the only reason we even consider running other people's code in the first place.
The time difference does matter though. There were some recent worm attacks in NPM that spread very quickly because they used post-install. I don’t remember how long it took NPM to block the packages but it was probably around 30 minutes or so? If it wasn’t for post-install then that same attack would have a much slower spread and thus a smaller blast radius.
> There's a huge difference, because postinstall scripts are almost guaranteed to run in your CI pipeline. Compromised code probably won't (maybe it will if your test cases test a compromised package). Different attack profile. Worse in some ways (your CI likely has NPM push tokens, which is how this single-package worm become a multi-package self-replicating worm) (your CI pipeline also likely has some level of privileged access to your cloud environment; deployed services are more likely to be highly scoped). But, better in some ways.
install scripts are a distraction, just like package signatures are a distraction. adding/removing either feature has no significant impact on the wormability of this package ecosystem. installed npm code is run, with nearly zero exceptions.
The installed code may be run in different settings, under a different user, with different privileges. Say, it may not run in CI/CD at all, or run only with the test user's privileges.
Postinstall scripts run at install time, with installer's privileges.
Trivial relative to which perspective? The distinction matters enough to care. Just because your father might give away their phone pin over the phone doesn't mean we should allow this granting remote access to his phone.
Trivial in the sense that in 99.9% of situations, "npm install" is immediately followed by "npm run", "npm test", or some form of execution. Any execution that imports a dependency is enough for a transitive dependency to execute its malicious payload immediately.
Post-install scripts have a slight edge over executing malicious code on import, i.e. they work 99.95% of the time instead of 99.9% of the time, but removing these scripts wouldn't materially change the situation we're in. You're locking the back door but leaving the front door and all of the windows wide open.
I'm going to suggest that we might be worse off in the short-medium term if post-install scripts are removed because everyone who thought that disabling post-install scripts was a "good enough" standalone security strategy will get caught with their pants down as attackers modify their payloads.
> Post-install scripts have a slight edge over executing malicious code on import, i.e. they work 99.95% of the time instead of 99.9% of the time
The "instead of" depends very much on the exploit and where it's wedged in the code. I doubt it's anywhere near 99%. Plus, getting the exploit to execute on the developer's machine is difficult to manage even in the best cases.
> because everyone who thought that disabling post-install scripts was a "good enough" standalone security strategy will get caught with their pants down as attackers modify their payloads.
Saying "well there are stupid people in the world" seems like a pretty bad justification to leave a hole open.
> The "instead of" depends very much on the exploit and where it's wedged in the code. I doubt it's anywhere near 99%. Plus, getting the exploit to execute on the developer's machine is difficult to manage even in the best cases.
We don't need to guess, it's going to be wedged in index.js, probably on line 1.
Are you aware that all transitive dependencies are executed immediately? You depend on PackageA which imports PackageB, which imports PackageC, which imports a trojanized PackageD. As soon as PackageD is imported, it executes its payload and infects your machine.
All of this happens in a blink of an eye, as soon as you run anything that kicks off an import chain containing a trojanized dependency.
Try it for yourself. This will simulate a malicious transitive dependency: koa > cookies > keygrip > tsscmp. You don't need to do anything except import koa.
mkdir demo && cd demo
npm install --save koa@3.2.0
echo 'import "koa";' > demo.mjs
echo 'console.log("\n\n--- pwned by a transitive dependency ---")' >> node_modules/tsscmp/lib/index.js
node demo.mjs
> Saying "well there are stupid people in the world" seems like a pretty bad justification to leave a hole open
Then you're calling much of the HN audience stupid. I've had this argument on here several times - and this is the top percentile of people who try to do something at all.
The justification for leaving this hole open is that it's a waste of time, resources, and mindshare patching a hole when there's a comparable and unpatchable hole right next to it. Advocate for things that actually work, like sandboxes.
> There's a huge difference, because postinstall scripts are almost guaranteed to run in your CI pipeline. Compromised code probably won't (maybe it will if your test cases test a compromised package). Different attack profile. Worse in some ways (your CI likely has NPM push tokens, which is how this single-package worm become a multi-package self-replicating worm) (your CI pipeline also likely has some level of privileged access to your cloud environment; deployed services are more likely to be highly scoped). But, better in some ways.
> Compromised code probably won't (maybe it will if your test cases test a compromised package).
Code runs automatically on import, you don't have to call dependency.infectMePlease()
Your code imports depA which imports depB which imports depC which imports depD which has been compromised, and boom, malicious code runs before you've even finished resolving the imports.
> your CI likely has NPM push tokens, which is how this single-package worm become a multi-package self-replicating worm
I've never once seen or worked with a CI pipeline that ran "npm install" that would be any safer if post-install scripts didn't exist. They all run "npm run test" or similar.
This doesn't really fix the issue though because package code is also executed at build time and during testing. Just maybe restricts the scope a little bit.
There's a huge difference, because postinstall scripts are almost guaranteed to run in your CI pipeline. Compromised code probably won't (maybe it will if your test cases test a compromised package). Different attack profile. Worse in some ways (your CI likely has NPM push tokens, which is how this single-package worm become a multi-package self-replicating worm) (your CI pipeline also likely has some level of privileged access to your cloud environment; deployed services are more likely to be highly scoped). But, better in some ways.
Its childish to believe that because you can't fix everything you shouldn't fix anything. Defense in depth.
> There's a huge difference, because postinstall scripts are almost guaranteed to run in your CI pipeline. Compromised code probably won't (maybe it will if your test cases test a compromised package)
You don't need to test a compromised package to have it execute code. Importing it anywhere in your tests is enough, even transitively.
It's for sure less likely to run but I doubt it's significantly different in practice.
