pnpm Has Lockfile Integrity Bypass that Allows Remote Dynamic Dependencies

Summary

HTTP tarball dependencies (and git-hosted tarballs) are stored in the lockfile without integrity hashes. This allows the remote server to serve different content on each install, even when a lockfile is committed.

Details

When a package depends on an HTTP tarball URL, pnpm's tarball resolver returns only the URL without computing an integrity hash:

resolving/tarball-resolver/src/index.ts:

return {
  resolution: {
    tarball: resolvedUrl,
    // No integrity field
  },
  resolvedVia: 'url',
}

The resulting lockfile entry has no integrity to verify:

remote-dynamic-dependency@http://example.com/pkg.tgz:
  resolution: {tarball: http://example.com/pkg.tgz}
  version: 1.0.0

Since there is no integrity hash, pnpm cannot detect when the server returns different content.

This affects:

• HTTP/HTTPS tarball URLs ("pkg": "https://example.com/pkg.tgz")
• Git shorthand dependencies ("pkg": "github:user/repo")
• Git URLs ("pkg": "git+https://github.com/user/repo")

npm registry packages are not affected as they include integrity hashes from the registry metadata.

PoC

See attached pnpm-bypass-integrity-poc.zip

The POC includes:

• A server that returns different tarball content on each request
• A malicious-package that depends on the HTTP tarball
• A victim project that depends on malicious-package

To run:

cd pnpm-bypass-integrity-poc
./run-poc.sh

The output shows that each install (with pnpm store prune between them) downloads different code despite having a committed lockfile.

Impact

An attacker who publishes a package with an HTTP tarball dependency can serve different code to different users or CI/CD environments. This enables:

• Targeted attacks based on request metadata (IP, headers, timing)
• Evasion of security audits (serve benign code during review, malicious code later)
• Supply chain attacks where the malicious payload changes over time

The attack requires the victim to install a package that has an HTTP/git tarball in its dependency tree. The victim's lockfile provides no protection.