Feeling the heat from Malicious Packages? Cool off with Cooldowns

Dependency cooldowns restrict package managers from installing versions released within a defined period, reducing exposure to newly published malicious dependencies while typically causing little developer disruption. The author describes implementing one-week cooldowns at Semgrep using Python’s uv package manager, where configuration settings require a sufficiently recent uv version and allow targeted exemptions for internal packages, registries without reliable timestamps, or recently adopted versions. The rollout began in familiar active repositories, supported by concise engineering communication, repository inventories created with Semgrep rules, and AI-assisted commands that updated manifests, lockfiles, CI configurations, Dockerfiles, and package-manager versions. As the effort expanded, Semgrep Agentic Workflows combined deterministic checks with Claude to automate repository discovery, exemption handling, lockfile validation, repairs, and pull-request creation, while Poetry support and registry-level exclusions broadened coverage. The experience also highlighted operational risks during package-manager migrations, the value of CI tests and fixing minor existing CI failures, and the benefit of archiving inactive repositories. Cooldowns are presented as a secure default rather than rigid governance, with exceptions available when developers need prompt access to security fixes, features, or internal releases.

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