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How I exploited NPM downloads... and why you shouldn't trust them

Andy Richardson on March 09, 2021

Over this past month, I've managed to get a package, with little to no users, to accumulate over one million downloads 🚀. It didn't cost any money...

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Oscar Franco • Mar 9 '21 • Edited

I don't get the logic here

Your argument is based on your exploit, which makes an illogical jump

I can spoof downloads -> Everyone spoofs -> the metric cannot be trusted

Unless you can proof a significant portion of users spoof (like in appstore reviews), then the argument is moot

Robert Myers • Mar 9 '21

You don't need a significant portion to spoof for the metric to be useless.

Let's say you need a package, you go look at exxpress. It has 30M downloads, therefore it's probably the popular package you wanted. So you're good to go with npm install exxpress right?

Andy Richardson • Mar 9 '21 • Edited

Your argument is based on your exploit, which makes an illogical jump

Sorry if I've made this unclear, there are two main points I'm trying to emphasise. Just in case you missed it 👇

But here's the thing, it isn't a useful metric for the following two reasons:

there is a loose (at best) relationship between users and download counts

the system is easily exploitable

In terms of the exploit side of things, my personal opinion is that data which can be manipulated to this degree shouldn't be given any weight.

Edit: I've updated the conclusion to remove the emphasis on the latter point - hope that clears up any confusion!

Olivier Guimbal • Mar 9 '21 • Edited

I agree... You could argue the same with security:

I can create an exploit in an npm package -> everyone does -> npm is fundamentally unsafe.

That is kind of true, but no one stops using npm for this reason. I guess the same goes for every metric. Who guarantees you that a project github stars dont come from a clickfarm ?

When using a npm package, you're trusting its author, to some extend.

(This is fun to see that npm doesnt even try to protect itself against this, though)

Ben Sinclair • Apr 27 '21

That's not what the post is getting at (to my reading). The equivalent would be, I think:

There happens to be wild fluctuations in the number of exploits accidentally appearing in npm packages due to cosmic rays -> I can demonstrate getting an exploit into an hyperbolic number of npm packages to prove a point -> npm is fundamentally unsafe.

It's talking about how the metric is useless even in telling you how many unique users downloaded a package, or how often something caches it or runs a build job.

Tierney Cyren • Mar 9 '21

While I've no doubt that NPM could create a popularity metric that aggregates a number of different attributes of a package (npms.io has already done it)

AFAIK the popularity metric that npm uses is from npms.io 😅

Andy Richardson • Mar 9 '21 • Edited

Do you have a source for this?

Looking at the package on npms.io it has a much lower popularity rating (3% compared to 14% on NPM).

Edit: just to clarify, I also had this assumption but assumed I was misremembering after seeing the difference.

Tierney Cyren • Mar 9 '21

The source I have is that I worked at a competitor when that change happened and was friends with folks at npm at the time. You're correct that there's apparently now deviation, and I'm not sure what that is - if npm continued using the original scoring and npms moved on, if npm moved on, or something else.

Maël Nison • Mar 9 '21

In this context however, the "caching" part of that description is rather noteworthy as it means the majority of downloads from yarn users won't contribute to download counts on NPM due to cache hits.

Slight correction - in 2017 we switched from a Cloudflare caching to a simple CNAME to the npm registry. So downloads via Yarn are counted just like any download from npm.