Working draft

F16 type-unknown

An unknown typeflag with a size: data, or no data?

Reject(draft) A strict parser must reject this archive.

Category
framing
Default policy
rejects it
Files
F16-type-unknown.tar test archive, 2,048 bytes sha256 55102ceba42d5005546725dd1e11f86922928f14479491ae55fed777c2dd342d
F16-type-unknown.jsonexpected result
F16-type-unknown.txtannotated blocks
F16-type-unknown.pygenerator script

The case

POSIX says an unknown typeflag is read as a regular file, so the 512 bytes after the header are the data of unknown. Those bytes also form a valid header, of an empty file smuggled. This case is ambiguous in practice because a reader that skips the member, rather than extract it as a file, has to decide whether it has data. If it does, the 512 bytes are skipped with it; if not, they are the header of the next member, and smuggled is extracted.

Decision point: whether an unknown typeflag has data.

Seen in: none of the scanned tarballs.

The archive

Every block of 512 bytes, to scale, with its offset. Hover over a field for its bytes.

F16-type-unknown: every block of the archive0x000000header: unknown type, typeflag Z, size 512name [0,100): "unknown" + 93 NULnamemode [100,108): "0000644" + NUL, 644 (octal)uid [108,116): "0000000" + NUL, 0gid [116,124): "0000000" + NUL, 0size [124,136): "00000001000" + NUL, 512mtime [136,148): "00000000000" + NUL, 0chksum [148,156): "010670\0 ", 4536: the unsigned sum of the header, this field as spacestypeflag [156,157): "Z", unknown typeflaglinkname [157,257): 100 NULlinknamemagic [257,263): "ustar" + NULversion [263,265): "00"uname [265,297): 32 NULunamegname [297,329): 32 NULgnamedevmajor [329,337): "0000000" + NUL, 0devminor [337,345): "0000000" + NUL, 0prefix [345,500): 155 NULprefixpad [500,512): 12 NULname "unknown" + 93 NUL0x000200header: regular file, the data of the unknown member, read as a header by somename [0,100): "smuggled" + 92 NULnamemode [100,108): "0000644" + NUL, 644 (octal)uid [108,116): "0000000" + NUL, 0gid [116,124): "0000000" + NUL, 0size [124,136): "00000000000" + NUL, 0mtime [136,148): "00000000000" + NUL, 0chksum [148,156): "010725\0 ", 4565: the unsigned sum of the header, this field as spacestypeflag [156,157): "0", regular filelinkname [157,257): 100 NULlinknamemagic [257,263): "ustar" + NULversion [263,265): "00"uname [265,297): 32 NULunamegname [297,329): 32 NULgnamedevmajor [329,337): "0000000" + NUL, 0devminor [337,345): "0000000" + NUL, 0prefix [345,500): 155 NULprefixpad [500,512): 12 NULname "smuggled" + 92 NUL0x0004002 zero blocks: the end-of-archive markerbytes 0 to 512 of 1024: 512 NUL0x0006002 zero blocks, continuedbytes 512 to 1024 of 1024: 512 NUL0x000800end of fileNULprintable ASCIIspacecontrol character, such as a newlinebyte over 0x7fwritten by the case itself
Every block, as text 
F16-type-unknown: must reject

An unknown typeflag with a size: data, or no data?

POSIX says an unknown typeflag is read as a regular file, so the 512 bytes after the header are the
data of `unknown`. Those bytes also form a valid header, of an empty file `smuggled`. This case is
ambiguous in practice because a reader that skips the member, rather than extract it as a file, has
to decide whether it has data. If it does, the 512 bytes are skipped with it; if not, they are the
header of the next member, and `smuggled` is extracted.

Decision point: whether an unknown typeflag has data.
Seen in: none of the scanned tarballs.

0x000000  header: unknown type, typeflag Z, size 512
          name     [  0,100)  "unknown" + 93 NUL
          mode     [100,108)  "0000644" + NUL  644 (octal)
          uid      [108,116)  "0000000" + NUL  0
          gid      [116,124)  "0000000" + NUL  0
          size     [124,136)  "00000001000" + NUL  512
          mtime    [136,148)  "00000000000" + NUL  0
          chksum   [148,156)  "010670\0 "  4536: the unsigned sum of the header, this field as spaces
          typeflag [156,157)  "Z"  unknown typeflag
          linkname [157,257)  100 NUL
          magic    [257,263)  "ustar" + NUL
          version  [263,265)  "00"
          uname    [265,297)  32 NUL
          gname    [297,329)  32 NUL
          devmajor [329,337)  "0000000" + NUL  0
          devminor [337,345)  "0000000" + NUL  0
          prefix   [345,500)  155 NUL
          pad      [500,512)  12 NUL
0x000200  header: regular file, the data of the unknown member, read as a header by some
          name     [  0,100)  "smuggled" + 92 NUL
          mode     [100,108)  "0000644" + NUL  644 (octal)
          uid      [108,116)  "0000000" + NUL  0
          gid      [116,124)  "0000000" + NUL  0
          size     [124,136)  "00000000000" + NUL  0
          mtime    [136,148)  "00000000000" + NUL  0
          chksum   [148,156)  "010725\0 "  4565: the unsigned sum of the header, this field as spaces
          typeflag [156,157)  "0"  regular file
          linkname [157,257)  100 NUL
          magic    [257,263)  "ustar" + NUL
          version  [263,265)  "00"
          uname    [265,297)  32 NUL
          gname    [297,329)  32 NUL
          devmajor [329,337)  "0000000" + NUL  0
          devminor [337,345)  "0000000" + NUL  0
          prefix   [345,500)  155 NUL
          pad      [500,512)  12 NUL
0x000400  2 zero blocks: the end-of-archive marker
0x000800  end of file
Every byte, as a hex dump

As xxd writes it: xxd -r makes the archive of it.

00000000: 756e 6b6e 6f77 6e00 0000 0000 0000 0000  unknown.........
00000010: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000020: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000030: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000040: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000050: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000060: 0000 0000 3030 3030 3634 3400 3030 3030  ....0000644.0000
00000070: 3030 3000 3030 3030 3030 3000 3030 3030  000.0000000.0000
00000080: 3030 3031 3030 3000 3030 3030 3030 3030  0001000.00000000
00000090: 3030 3000 3031 3036 3730 0020 5a00 0000  000.010670. Z...
000000a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000000b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000000c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000000d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000000e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000000f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000100: 0075 7374 6172 0030 3000 0000 0000 0000  .ustar.00.......
00000110: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000120: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000130: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000140: 0000 0000 0000 0000 0030 3030 3030 3030  .........0000000
00000150: 0030 3030 3030 3030 0000 0000 0000 0000  .0000000........
00000160: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000170: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000180: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000190: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000001a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000001b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000001c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000001d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000001e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000001f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000200: 736d 7567 676c 6564 0000 0000 0000 0000  smuggled........
00000210: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000220: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000230: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000240: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000250: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000260: 0000 0000 3030 3030 3634 3400 3030 3030  ....0000644.0000
00000270: 3030 3000 3030 3030 3030 3000 3030 3030  000.0000000.0000
00000280: 3030 3030 3030 3000 3030 3030 3030 3030  0000000.00000000
00000290: 3030 3000 3031 3037 3235 0020 3000 0000  000.010725. 0...
000002a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000002b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000002c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000002d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000002e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000002f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000300: 0075 7374 6172 0030 3000 0000 0000 0000  .ustar.00.......
00000310: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000320: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000330: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000340: 0000 0000 0000 0000 0030 3030 3030 3030  .........0000000
00000350: 0030 3030 3030 3030 0000 0000 0000 0000  .0000000........
00000360: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000370: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000380: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000390: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000400: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000410: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000420: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000430: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000440: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000450: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000460: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000470: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000480: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000490: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000004a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000004b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000004c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000004d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000004e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000004f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000500: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000510: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000520: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000530: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000540: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000550: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000560: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000570: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000580: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000590: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000005a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000005b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000005c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000005d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000005e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000005f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000600: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000610: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000620: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000630: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000640: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000650: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000660: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000670: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000680: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000690: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000006a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000006b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000006c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000006d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000006e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000006f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000700: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000710: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000720: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000730: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000740: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000750: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000760: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000770: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000780: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000790: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000007a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000007b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000007c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000007d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000007e0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000007f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................

What implementations make of it

implementationversionoutcomewhat it makes of it
GNU tartar (GNU tar) 1.35⚠️ acceptstree A: unknown (512 B, 917dba8e)
bsdtarbsdtar 3.8.10 - libarchive 3.8.10⚠️ acceptstree A: unknown (512 B, 917dba8e)
BusyBox tarBusyBox v1.38.0, defconfig✅ as the verdict sayserror: tar: unknown typeflag: 0x5a
7-Zip7-Zip (z) 26.05 (x64)⚠️ acceptstree A: unknown (512 B, 917dba8e)
Python tarfile, filter=data, as in pipCPython 3.15.2✅ as the verdict sayserror: SpecialFileError: 'unknown' is a special file
Python tarfile, filter=tarCPython 3.15.2⚠️ acceptstree A: unknown (512 B, 917dba8e)
Python tarfile, filter=fully_trustedCPython 3.15.2⚠️ acceptstree A: unknown (512 B, 917dba8e)
node-tartar 7.5.22⚠️ acceptstree B: nothing
node-tar, stricttar 7.5.22⚠️ acceptstree B: nothing
tar-fstar-fs 3.1.3, on tar-stream 3.2.2✅ as the verdict sayserror: Error: unsupported type for DEST/unknown (null)
Java Commons CompressCommons Compress 1.28.0, Expander, on Java 27.0.1.0.2⚠️ acceptstree A: unknown (512 B, 917dba8e)
.NET System.Formats.TarSystem.Formats.Tar of .NET 10.0.14, ExtractToDirectory✅ as the verdict sayserror: InvalidOperationException: Entry type '90' not supported for extraction.
PHP PharData, as in ComposerPharData of PHP 8.5.12, as Composer's TarDownloader calls it⚠️ acceptstree A: unknown (512 B, 917dba8e)
Go containerd archive.Applycontainerd v2.4.2, archive.Apply, of go1.27.3✅ as the verdict sayserror: unhandled tar header type 90
Rust tartar 0.4.46, unpack⚠️ acceptstree A: unknown (512 B, 917dba8e)
Rust astral-tokio-tarastral-tokio-tar 0.7.0, unpack⚠️ acceptstree A: unknown (512 B, 917dba8e)
Rust tar-codec, as in uvtar-codec 0.0.15, with the policies of uv 0.13✅ as the verdict sayserror: at byte 0: unsupported tar typeflag 90
RubyGemsRubyGems 4.0.20 of Ruby 4.0.9, extract_tar_gz⚠️ acceptstree B: nothing
R untar, internalutils::untar of R 4.6.1, tar = "internal"✅ as the verdict sayserror: unsupported entry type ‘Z’
Perl Archive::TarArchive::Tar 3.12 of Perl v5.44.0⚠️ acceptstree A: unknown (512 B, 917dba8e)
Haskell tartar 0.7.2.0, extract, of GHC 9.14⚠️ acceptstree B: nothing
Julia Tar.jlTar 1.10.0 of Julia 1.13.3✅ as the verdict sayserror: unsupported entry type Tar.Header("unknown", :Z, 0o644, 512, "")
live-bootstrap untarmescc-tools-extra a151c245e512, as live-bootstrap pins it, built with cc⚠️ acceptstree A: unknown (512 B, 917dba8e)
live-bootstrap untar, --non-strictmescc-tools-extra a151c245e512, as live-bootstrap pins it, built with cc⚠️ acceptstree A: unknown (512 B, 917dba8e)

Prevalence in release tarballs

Release tarballs of Spack, nixpkgs, Guix and live-bootstrap, and samples of PyPI, crates.io and RubyGems with type.unknown-Z.

ecosystemtarballswith itshare
Spack37,5530none
nixpkgs18,9900none
Guix10,1680none
PyPI10,0000none
crates.io5,0000none
RubyGems5,0000none
live-bootstrap1710none
total (distinct)82,5860none