Defending Your Rails App: Enabling Dependency Cooldowns to Prevent Supply Chain Attacks

On March 31, 2026, a North Korean state actor hijacked the npm account of an Axios maintainer and published two backdoored versions of one of the world's most popular JavaScript libraries — a package downloaded over 100 million times per week. The malicious versions introduced a hidden dependency that silently installed a cross-platform remote access trojan. The compromised packages were live for roughly three hours before removal, but in that window, hundreds of thousands of installs had already occurred.

One week earlier, the LiteLLM Python package suffered a similar fate. An attacker compromised the project's CI/CD pipeline through a poisoned Trivy security scanner, exfiltrated the PyPI publish token, and pushed two malicious versions that deployed a three-stage payload targeting cloud credentials, SSH keys, and Kubernetes clusters. LiteLLM is downloaded 3.4 million times per day — the malicious versions were live for just 40 minutes.

These are not theoretical risks, and they are not limited to JavaScript or Python. Every package ecosystem that allows instant publishing shares the same attack surface: a single compromised maintainer account can push malicious code that reaches thousands of production applications before anyone notices. The Ruby ecosystem is no exception. The rest-client gem was backdoored through an account hijack in 2019, and strong_password carried a remote code execution payload that went undetected for six months in 2020.

The common thread across all of these incidents is time. Most malicious packages are detected and removed within hours or days. A simple delay between publication and installation — a cooldown — would have blocked every one of them.

This post aims to walk you through a practical, layered approach to defending your Rails application against these attacks using dependency cooldowns — a deliberate waiting period before your project adopts newly published gem versions.

Understanding Dependency Cooldowns

A dependency cooldown introduces a time buffer between when a gem version is published to a registry and when it becomes installable in your project. Think of it as a quarantine period. Most malicious packages are detected and removed from registries within hours or days of publication. A 48-hour or 7-day cooldown means your application never touches packages during their most dangerous window.

The JavaScript ecosystem has embraced this concept aggressively. npm shipped min-release-age in v11.10.0, pnpm added minimumReleaseAge, and Bun followed suit. The Ruby ecosystem is now catching up, and there are two complementary strategies available today: gem.coop's registry-level cooldowns and Dependabot's cooldown configuration.

Approach 1: Registry-Level Cooldowns with gem.coop

The Gem Cooperative is a community-run gem server maintained by former RubyGems core contributors. Their cooldowns beta enforces a 48-hour delay at the registry level, meaning newly published gem versions are hidden from your Bundler resolution entirely until they have aged past the threshold.

The elegance of this approach is that it requires no changes to Bundler itself. By pointing your gem source at the cooldown endpoint, any Bundler user gets cooldowns without changing their tooling or workflow.

Configuration 

Update the source in your Gemfile:

That single line change ensures every gem resolved through this source must have been published at least 48 hours ago. No gem-level configuration is needed — the filtering happens at the index level before Bundler ever sees the package.

Bypassing Cooldowns for Security Fixes 

There will be times when you need to pull in a gem version immediately — a critical CVE patch, for example. gem.coop supports a dual-source approach for exactly this scenario:

In this configuration, nokogiri is pulled directly from the primary gem.coop server without any cooldown delay, while all other gems go through the 48-hour waiting period. We recommend treating this as an escape hatch rather than a default workflow. If you find yourself bypassing cooldowns frequently, it may be worth re-evaluating your update cadence.

Verifying the Configuration 

After updating your Gemfile, run a fresh bundle to confirm resolution works correctly:

You can verify which source each gem is resolved from by inspecting the lockfile:

The SOURCES section at the top of your Gemfile.lock will reflect the gem.coop endpoint.

Approach 2: Dependabot Cooldowns

If your team uses GitHub's Dependabot for automated dependency updates, you can configure a cooldown period directly in your Dependabot configuration. This delays the creation of version-update pull requests until a gem version has been published for a minimum number of days.

We recommend this approach as a complement to gem.coop, not a replacement. Dependabot cooldowns protect your automated update pipeline, while gem.coop cooldowns protect every bundle install across local development and CI.

Configuration 

Add a cooldown block to your .github/dependabot.yml:

This configuration tells Dependabot to wait 7 days by default before opening a PR for a new gem version. Major version bumps get a more conservative 14-day window, while patch releases can flow through after 3 days.

A critical detail: cooldowns apply only to version updates, not security updates. If a CVE is published and a patched gem version is available, Dependabot will still open a PR immediately. This gives you the best of both worlds — routine updates are gated, but urgent security patches flow through without delay.

Tuning the Window 

The right cooldown period depends on your team's risk tolerance and update cadence. Here is a reasonable starting point:

For teams on a monthly update cadence, a flat default-days: 7 is often sufficient. If your team merges dependency PRs daily, the per-semver granularity helps avoid unnecessary delays on low-risk patches.

Approach 3: Bundler Checksum Verification

Cooldowns protect against newly published malicious versions, but they do not protect against tag hijacking — where an attacker replaces the contents of an existing version. Bundler 2.6+ introduced checksum verification to address this gap.

Enable it by running:

With this enabled, Bundler calculates cryptographic hashes for each gem and stores them in Gemfile.lock. On subsequent installs, it verifies that the downloaded gem matches the expected hash. If the contents have changed, the install fails.

We recommend enabling checksum verification alongside cooldowns. Together, they cover two distinct attack vectors: cooldowns block short-lived malicious releases, and checksums detect tampering with existing versions.

Putting It All Together

A complete defensive setup for a Rails application combines all three layers. Your Gemfile uses the gem.coop cooldown source:

Your .github/dependabot.yml enforces cooldowns on automated PRs:

And Bundler checksum verification is enabled globally:

This layered approach means:

Limitations Worth Knowing

Cooldowns are not a silver bullet. They are highly effective against the most common attack pattern — compromised maintainer accounts publishing short-lived malicious releases — but they do not address:

We recommend pairing cooldowns with bundler-audit in your CI pipeline for complete coverage:

Looking Ahead

The momentum behind dependency cooldowns is accelerating across every major ecosystem. In a six-month span from late 2025 through early 2026, five JavaScript package managers shipped native cooldown support: pnpm, Yarn, Bun, Deno, and npm. Python's uv added relative duration support, and pip shipped --uploaded-prior-to in v26.0. Cargo has an RFC in progress with registry-side infrastructure stabilized in Cargo 1.94.

Ruby's story is more nuanced. Bundler and RubyGems do not yet have native cooldown support, and there is no open feature request on the ruby/rubygems repository tracking this functionality. The Bundler 4 roadmap focuses on lockfile improvements and dependency resolution performance, but does not mention release-age gating. For now, the Ruby community's answer comes from outside core tooling: gem.coop's registry-level cooldowns and Dependabot's bot-layer delays.

This is worth watching. The gem.coop team — several of whom are former RubyGems core maintainers who departed during the September 2025 governance crisis — are well-positioned to push the conversation forward. Their approach of implementing cooldowns at the index level rather than the client level sidesteps the need for Bundler changes entirely, which may prove to be the more practical path for the Ruby ecosystem.

For now, the combination of gem.coop, Dependabot cooldowns, and checksum verification gives Rails teams a practical, defense-in-depth posture. A 7-day cooldown would have blocked the Axios compromise (3 hours), the LiteLLM attack (40 minutes), and every major Ruby gem incident in recent memory. The cost is a one-time configuration change. The protection is continuous.