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If an npm or PyPI update looks suspicious, keep the last known-good manifest and lockfile intact, inspect the proposed changes before installing, and separate read-only checks from commands that modify dependencies. A lockfile, vulnerability scan, signature, or provenance record can provide useful evidence—but none alone proves a release is safe. This workflow helps you investigate first and test any eventual change without disrupting the working build.
1. Preserve the known-good build
Before changing dependencies, record the package name, current and proposed versions, when and where the update appeared, and the environment in which the build last passed. Preserve the manifest, lockfile, and relevant CI logs in version control or another reviewable record. Avoid broad updates and automated fixes until you have inspected the proposed change. This gives you a comparison point; it does not certify that the existing dependency set is safe.
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2. Review the manifest and lockfile diff
Inspect both the direct dependency declaration and the lockfile. Look for changed resolved versions, new transitive dependencies, registry or tarball URL changes, integrity values, platform-specific artifacts, and unexpected substitutions. A lockfile makes the dependency resolution reviewable and repeatable, but it can also lock an exact malicious artifact.
For npm, the package-lock file drives npm install when its resolved versions satisfy the ranges in package.json. Use npm ci in workflows that require strict synchronization between the manifest and lockfile; it is intended for clean, reproducible installs and does not update the lockfile. See npm install and npm ci documentation for version-specific behavior.
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3. Check vulnerability advisories without treating them as malware detection
npm audit asks the configured registry for known vulnerability information. Review the affected package, version range, dependency path, and whether that path applies to your project. A clean result means no matching known advisory was returned in that audit context; it does not establish that the package is benign.
Keep inspection separate from remediation. npm audit fix changes the dependency tree and, as npm documents, runs a full npm install under the hood. Review the proposed changes before applying fixes, especially when remediation entails a major version change. See npm audit.
4. Compare the candidate release with the previous one
Before executing candidate code, compare the published artifact and release context with the prior version and the project’s expected release process. These checks are investigation leads, not a validated malware-detection checklist.
- Publisher and project continuity: Check maintainers or publishers, repository information, tags or commits, release timing, and provenance for unexpected changes.
- Dependency changes: Identify new or substituted transitive packages, as well as changes to registry and tarball locations.
- Package contents: Compare files and metadata. Pay particular attention to new install scripts, generated or minified payloads, unexplained files, and code that introduces unexpected network, file-system, or process behavior.
- Python build requirements: For a source distribution, inspect the build configuration and declared build-backend requirements.
- Advisory and compatibility evidence: Check known advisories and the dependency path, then consider your Node or Python version, platform, native dependencies, and build workflow.
Hashes, signatures, and provenance are pieces of evidence, not safety verdicts. A hash fetched from the same package index as the artifact can help detect corruption, but it is not independent proof that the publisher did not upload a malicious file. PyPI’s documentation explains the limit directly: “An attestation will tell you where a PyPI package came from, but not whether you should trust it.” See PyPI’s security model and considerations. npm provides signature and provenance verification through npm audit signatures; verification can help establish integrity or origin but does not prove benign intent. See npm audit.
5. Treat installation and builds as code-execution boundaries
npm lifecycle scripts
npm packages can run lifecycle scripts during installation. npm exposes controls such as ignore-scripts and script-approval settings; their availability and effects depend on your npm version and project configuration. Disabling scripts can break legitimate installs or builds, so check the current configuration rather than assuming a setting is active. Avoid dangerous overrides that bypass script-approval policy. See npm install and npm config.
PyPI source distributions
pip builds source distributions using a build backend and installs build-time dependencies into an isolated temporary environment. That isolation separates build dependencies from the runtime environment; it does not make arbitrary build code trustworthy. Do not disable build isolation as a general security fix: pip says that users who do so become responsible for managing build dependencies. See pip’s build-system interface documentation.
If execution is necessary
Use a disposable, isolated environment with no credentials and no access to production systems. Preserve logs and artifact hashes. Isolation is a conservative precaution, not a guarantee that every payload will be contained.
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For npm projects
Retain the lockfile and use the install command that matches the project’s workflow. In CI, npm ci enforces strict manifest-and-lockfile synchronization rather than resolving a changed tree. Review lockfile changes before merging, and avoid unreviewed broad updates as a way to find out whether a release works.
For pip projects
Pin requirements to specific versions and, where practical, specify hashes in a requirements file. pip’s hash-checking mode, enabled with --require-hashes, requires pinned requirements and hashes throughout the dependency set; hashes copied from the same remote index as the download are not independent evidence of publisher intent. --only-binary :all: can prevent installing source distributions, but may make a package unavailable if no compatible wheel exists. See pip’s secure installs guidance.
Test a proposed change deliberately
Once the release has been investigated, test an upgrade in a branch or isolated CI job. Run the project’s relevant build and tests, inspect the resulting lockfile diff, and merge intentionally. No checklist can guarantee compatibility: results depend on the project’s language versions, platform, native dependencies, and workflow.
7. Report credible evidence of malware
If you find credible evidence, preserve the exact package version, artifact hash, source URL, and reproducible details where safe. Do not publish credentials, live payloads, or sensitive indicators unnecessarily; follow the registry’s current reporting process.
Report to npm
npm asks reporters to identify the package and all affected versions, describe the behavior, and provide supporting references, commits, or code examples. npm states: “If you find malware in a package (either yours or someone else’s), you can report it to the npm Security team to help keep the JavaScript ecosystem safe.” Use npm’s malware reporting guidance.
Report to PyPI
PyPI provides a project malware-reporting flow that asks for an explanation and links to problematic lines in distributions through Inspector. PyPI’s security policy says suspected security issues should not be posted in public forums. Follow the PyPI security policy and its reporting instructions.
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