On June 3rd, Bundler 4.0.13 shipped a feature called cooldown. The release post described the problem it solves like this: "an account is compromised, a malicious version ships, and any bundle install in the minutes that follow resolves straight to it."
Forty-five days later, someone did exactly that to three gems.
Aikido Security disclosed the campaign on July 19th and named it SleeperGem: malicious versions of git_credential_manager, Dendreo, and fastlane-plugin-run_tests_firebase_testlab. Two of those gems had sat untouched since 2019 and 2020, which is where the name comes from. (The third impersonates Microsoft's Git Credential Manager, and no report says whether that account was hijacked or simply the attacker's.)
The clever part is what the payload does when it lands. Aikido found a skip_install? check that "scans for roughly 30 environment variables belonging to CI platforms, GitHub Actions, GitLab CI, CircleCI, Travis, Jenkins, Vercel, and does nothing if it spots one." It sits still in your pipeline and wakes up on your laptop. StepSecurity reversed the native binary it drops: a daemon in ~/.local/share/gcm/, a systemd user unit, a cron entry, and if you installed as root, a setuid shell at /usr/local/sbin/ping6.
