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A more secure bundler: We fixed our source priorities.

by David Rodríguez on

NOTE: Whereas the issue was initially fixed in bundler 2.2.10, it had to be reverted due to several problems caused by the initial approach. A proper fix was finally released with bundler 2.2.18.

What happened?

Last week an article about “Dependency Confusion” hit the news, where a developer was able to make thousands of dollars on bug bounty programs from big tech companies, by pushing libraries to public repositories that ended up unintentionally being installed into these companies servers.

The developer was able to expose (in a non-malicious way) a vulnerability present in well-known dependency managers, where given a library name they will end up preferring installing it from a public source rather than from a private source. This is not secure because the name in the public source is controlled by the first person claiming it, whereas the name in the private source is controlled by the private source owner.

Unfortunately, Bundler had this vulnerability.

There’s good news though:

Things were safe on the side

The organization, in collaboration with, have a pretty good malicious code detection system. In fact, the only reason this developer was able to make all this money by getting these gems installed in companies private servers is because our system detected them, flagged them for us, and we determined them to be non-malicious, and only for research purposes. If those gems had been malicious, we wouldn’t have allowed them.

Check out the more detailed blog post from our friends about what happened in the side of things, and how things were secure.

The issue has been fixed in bundler 2.2.10

We have shipped bundler 2.2.10 with a fix, and now whenever you specify a block source in your Gemfile, bundler will prioritize it when resolving direct dependencies specified inside, and also transitive dependencies of those. So in the following situation both my-private-gem and my-another-private-gem will be picked up from https://my-private-server, even if someone pushes a higher version with the same name to

# my-private-gem.gemspec
# ...
# Gemfile

source ""

source "https://my-private-server" do
  gem "my-private-gem"

Make sure you upgrade your bundler version either by running gem install bundler, or by upgrading rubygems through gem update --system (which will install bundler 2.2.10 as a default gem).

Final notes

The bundler team had actually been aware of this issue for a while, but unfortunately lacks resources to take care of everything we need to take care, so the fix was postponed for too long. Maintaining the infrastructure and its client libraries requires a big amount of work and we barely manage to keep up with it. So, if your company really needs us to stay on top of these issues, please consider funding RubyTogether ❤️.

That’s all for today,

Happy bundling!

Deivid, André and the RubyGems team