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bdu:2026-00957

BREW-pnpm-CVE-2026-23888 — pnpm: Binary ZIP extraction allows arbitrary file write via path traversal (Zip Slip)

Affected: Homebrew: pnpm

pnpm is a package manager. Prior to version 10.28.1, a path traversal vulnerability in pnpm's binary fetcher allows malicious packages to write files outside the intended extraction directory. The vulnerability has two attack vectors: (1) Malicious ZIP entries containing `../` or absolute paths that escape the extraction root via AdmZip's `extractAllTo`, and (2) The `BinaryResolution.prefix` field is concatenated into the extraction path without validation, allowing a crafted prefix like `../../evil` to redirect extracted files outside `targetDir`. The issue impacts all pnpm users who install packages with binary assets, users who configure custom Node.js binary locations and CI/CD pipelines that auto-install binary dependencies. It can lead to overwriting config files, scripts, or other sensitive files leading to RCE. Version 10.28.1 contains a patch.

EUVD-2026-266765

fkie_cve-2026-23888

GHSA-6pfh-p556-v868 — pnpm: Binary ZIP extraction allows arbitrary file write via path traversal (Zip Slip)

Affected: npm: pnpm

### Summary

A path traversal vulnerability in pnpm's binary fetcher allows malicious packages to write files outside the intended extraction directory. The vulnerability has two attack vectors: (1) Malicious ZIP entries containing `../` or absolute paths that escape the extraction root via AdmZip's `extractAllTo`, and (2) The `BinaryResolution.prefix` field is concatenated into the extraction path without validation, allowing a crafted prefix like `../../evil` to redirect extracted files outside `targetDir`.

### Details

The vulnerability exists in the binary fetching and extraction logic:

**1. Unvalidated ZIP Entry Extraction (`fetching/binary-fetcher/src/index.ts`)**

AdmZip's `extractAllTo` does not validate entry paths for path traversal:

```typescript const zip = new AdmZip(buffer) const nodeDir = basename === '' ? targetDir : path.dirname(targetDir) const extractedDir = path.join(nodeDir, basename) zip.extractAllTo(nodeDir, true) // Entry paths not validated! await renameOverwrite(extractedDir, targetDir) ```

A ZIP entry with path `../../../.npmrc` will be written outside `nodeDir`.

**2. Unvalidated Prefix in BinaryResolution (`resolving/resolver-base/src/index.ts`)**

The `basename` variable comes from `BinaryResolution.prefix` and is used directly in path construction:

```typescript const extractedDir = path.join(nodeDir, basename) // If basename is '../../evil', this points outside nodeDir ```

### PoC

**Attack Vector 1: ZIP Entry Path Traversal**

```pytho…