pnpm: Project env lockfile can short-circuit package-manager resolution and execute lockfile-selected pnpm bytes

The full patched replay for the shared branch passed with all 20 candidates marked fixed. This candidate's replay evidence is results/CAND-PNPM-063-patched-result.json.

Summary

pnpm can persist package-manager bootstrap metadata in the first YAML document of pnpm-lock.yaml. Before the patch, direct pnpm execution trusted an already resolved packageManagerDependencies entry when the committed env lockfile contained matching pnpm and @pnpm/exe versions. A malicious repository could therefore commit package-manager lockfile package records and snapshots that bypassed fresh package-manager resolution, then cause pnpm to install and execute bytes selected by that committed lockfile state during automatic version switching.

Details

The vulnerable source-to-sink path was:

• lockfile/fs/src/envLockfile.ts reads the repository's first YAML lockfile document and validates shape only.
• pnpm/src/main.ts reaches switchCliVersion() when a direct pnpm invocation sees a wanted pnpm package manager with onFail=download.
• pnpm/src/switchCliVersion.ts reads the committed env lockfile when package-manager metadata should be persisted.
• installing/env-installer/src/resolvePackageManagerIntegrities.ts treated packageManagerDependencies as resolved when only the pnpm and @pnpm/exe versions matched.
• engine/pm/commands/src/self-updater/installPnpm.ts converts env-lockfile snapshots and packages into the wanted lockfile used by headlessInstall().
• pnpm/src/switchCliVersion.ts executes the installed pnpm binary with spawn.sync().

The helper fast path is intentionally still version-based for non-execution callers, so the security boundary is enforced at the execution path: switchCliVersion() now re-resolves already present package-manager env-lockfile entries before they can reach installPnpmToStore() and spawn.sync().

PoC

Standalone PoC and verification script:

The PoC constructs a committed env-lockfile object with matching package-manager dependency versions and attacker-selected package metadata:

{
  "importers": {
    ".": {
      "configDependencies": {},
      "packageManagerDependencies": {
        "@pnpm/exe": { "specifier": "9.3.0", "version": "9.3.0" },
        "pnpm": { "specifier": "9.3.0", "version": "9.3.0" }
      }
    }
  },
  "lockfileVersion": "9.0",
  "packages": {
    "/[email protected]": {
      "resolution": {
        "integrity": "sha512-poisoned"
      }
    }
  },
  "snapshots": {
    "/[email protected]": {}
  }
}

Pre-patch exploit model:

1. The victim runs pnpm directly in a malicious repository.
2. The requested package-manager version differs from the currently running pnpm.
3. pnpm enters switchCliVersion() and reads the committed env lockfile.
4. Matching pnpm / @pnpm/exe versions short-circuit package-manager resolution.
5. pnpm installs from the committed env-lockfile package records and executes the resulting pnpm binary.

Observed primitive proof from the PoC:

{
  "primitive": "unforced resolver reuses already-resolved env lockfile metadata",
  "isResolvedByVersionOnly": true,
  "reusedPoisonedIntegrity": true
}

The same script then runs the patched switchCliVersion regression. The regression seeds a poisoned committed env lockfile, has the resolver return a trusted replacement lockfile, and asserts installPnpmToStore() receives the trusted lockfile rather than the committed one. This would fail on the vulnerable control flow because the resolver was not called and the committed lockfile reached the installer.

Focused validation commands:

./node_modules/.bin/tsgo --build installing/env-installer/tsconfig.json
./node_modules/.bin/tsgo --build pnpm/tsconfig.json
PNPM_REGISTRY_MOCK_PORT=7799 NODE_OPTIONS="--experimental-vm-modules --disable-warning=ExperimentalWarning --disable-warning=DEP0169" ../node_modules/.bin/jest src/switchCliVersion.test.ts -t "re-resolved package-manager lockfile" --runInBand
PNPM_REGISTRY_MOCK_PORT=7799 NODE_OPTIONS="--experimental-vm-modules --disable-warning=ExperimentalWarning --disable-warning=DEP0169" ../node_modules/.bin/jest src/switchCliVersion.test.ts src/syncEnvLockfile.test.ts --runInBand
./node_modules/.bin/eslint installing/env-installer/src/resolvePackageManagerIntegrities.ts pnpm/src/switchCliVersion.ts pnpm/src/switchCliVersion.test.ts
git diff --check

Validation result:

• The PoC confirmed the unforced resolver still reuses a version-matching env lockfile, proving the original primitive.
• Patched switchCliVersion() calls resolvePackageManagerIntegrities() with force: true when committed env-lockfile package-manager entries already satisfy the requested version.
• Patched switchCliVersion() assigns the resolver return value back to envLockfile.
• The installer receives the refreshed lockfile and not the poisoned committed lockfile.
• TypeScript builds passed for @pnpm/installing.env-installer and pnpm.
• The focused Jest regression passed: 1 passed, 1 skipped in switchCliVersion.test.ts.
• ESLint passed for the affected package-manager switch files.
• git diff --check passed.

Impact

A malicious repository can cause arbitrary package-manager code execution in the victim's developer or CI environment before normal command handling continues. That code executes with the victim user's privileges and can read local secrets, alter project files, mutate dependency state, or run further commands.

Affected products

Ecosystem: npm

Package name: pnpm, @pnpm/installing.env-installer

Affected versions: current main before this patch; direct pnpm execution with package-manager auto-switching and a repository-controlled env lockfile.

Patched versions: pending release containing this patch.

Severity

Severity: High

Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Base score: 8.8

Rationale: the malicious source is repository-controlled package-manager lockfile state delivered through normal supply-chain channels. Exploitation is low complexity once the victim runs pnpm directly, no attacker privileges are required, and user interaction is required. Successful exploitation executes attacker-selected package-manager code in the victim user's security context, with high confidentiality, integrity, and availability impact.

Weaknesses

CWE-829: Inclusion of Functionality from Untrusted Control Sphere

CWE-494: Download of Code Without Integrity Check

CWE-345: Insufficient Verification of Data Authenticity

Patch

The patch makes automatic package-manager switching re-resolve repository-provided bootstrap metadata before install and execution:

• resolvePackageManagerIntegrities() accepts force, which bypasses the version-only fast path.
• switchCliVersion() creates a store controller even when the committed env lockfile already contains satisfying package-manager dependency versions.
• switchCliVersion() calls resolvePackageManagerIntegrities() with force: true for already resolved package-manager entries.
• switchCliVersion() assigns the returned env lockfile back to envLockfile, so installPnpmToStore() installs from freshly resolved metadata.
• The package-manager bootstrap registry hardening from CAND-PNPM-061 is reused, so the refresh happens through trusted package-manager registries rather than repository workspace registries.

Changed files:

• installing/env-installer/src/resolvePackageManagerIntegrities.ts
• pnpm/src/switchCliVersion.ts
• pnpm/src/switchCliVersion.test.ts

Changeset:

• .changeset/clean-package-manager-registries.md

Pacquet parity:

No pacquet-side patch is required for this finding because pacquet does not implement pnpm's package-manager auto-switch path or installPnpmToStore().

CVSS Reassessment

Initial CVSS remains correct for vulnerable versions: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H / 8.8 High.

Final CVSS after patch: not vulnerable after patch / 0.0. The PoC still demonstrates the underlying unforced env-lockfile reuse primitive, but the patched execution path force-refreshes package-manager metadata through trusted bootstrap registries before install or execution.

Remaining Risk

The helper resolvePackageManagerIntegrities() still has an unforced fast path that treats matching pnpm and @pnpm/exe versions as resolved. Current execution-sensitive callers either use trusted roots/registries or pass through the patched switchCliVersion() boundary, but future execution paths should use force: true before installing or executing package-manager bytes from repository-provided env-lockfile metadata.