N35 symlink-escapes · Tar file extraction test suite

The archive has one member, a symlink link to ../escaped, and does not write through it.

The default policy tolerates it, and rejects an archive that writes through a symlink.

path	kind	contents
`link`	symlink	→ `../escaped`

Decision point: whether a symlink that points out of the destination is created.

The archive¶

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

What implementations make of it¶

In the outcome column, ✅ means that the implementation follows the default policy.

implementation	version	outcome	what it makes of it
GNU tar	tar (GNU tar) 1.35	➕ accepts	the expected tree
bsdtar	bsdtar 3.8.11 - libarchive 3.8.11	➕ accepts	the expected tree
BusyBox tar	BusyBox v1.38.0, defconfig	➕ accepts	the expected tree
7-Zip	7-Zip (z) 26.05 (x64)	➖ rejects	error: ERROR: Dangerous link path was ignored : link : ../escaped
Python tarfile, filter=data, as in pip	CPython 3.15.2	➖ rejects	error: LinkOutsideDestinationError: 'link' would link to 'ROOT/x/y/escaped', which is outside the destination
Python tarfile, filter=tar	CPython 3.15.2	➕ accepts	the expected tree
Python tarfile, filter=fully_trusted	CPython 3.15.2	➕ accepts	the expected tree
node-tar	tar 7.5.22	❌ another tree, or rejects	tree A: nothing
node-tar, strict	tar 7.5.22	➖ rejects	error: Error: TAR_ENTRY_ERROR: linkpath escapes extraction directory
tar-fs	tar-fs 3.1.3, on tar-stream 3.2.2	➖ rejects	error: Error: DEST/link is not a valid symlink
Java Commons Compress	Commons Compress 1.28.0, Expander, on Java 27.0.1.0.2	❌ another tree, or rejects	tree B: `link` (0 B, e3b0c442)
.NET System.Formats.Tar	System.Formats.Tar of .NET 10.0.14, ExtractToDirectory	➖ rejects	error: IOException: Extracting the Tar entry '../escaped' would have resulted in a link target outside the specified destination directory: 'DEST/'
PHP PharData, as in Composer	PharData of PHP 8.5.12, as Composer's TarDownloader calls it	❌ another tree, or rejects	tree B: `link` (0 B, e3b0c442)
Go containerd archive.Apply	containerd v2.4.2, archive.Apply, of go1.27.3	➕ accepts	the expected tree
Rust tar	tar 0.4.46, unpack	➕ accepts	the expected tree
Rust astral-tokio-tar	astral-tokio-tar 0.7.1, unpack	➕ accepts	the expected tree
Rust tar-codec, as in uv	tar-codec 0.0.16, with the policies of uv 0.13	➖ rejects	error: at byte 0: unsafe symbolic-link target "../escaped": escapes the destination root
RubyGems	RubyGems 4.0.20 of Ruby 4.0.9, extract_tar_gz	➖ rejects	error: Gem::Package::SymlinkError: installing symlink 'link' pointing to parent path ROOT/x/y/escaped of DEST is not allowed
R untar, internal	utils::untar of R 4.6.2, tar = "internal"	➕ accepts	the expected tree
Perl Archive::Tar	Archive::Tar 3.12 of Perl v5.44.0	➖ rejects	error: Symlink 'link' target attempts traversal. Not extracting under SECURE EXTRACT MODE at contrib/matrix/runners/perl/extract.pl line 14. Could not extract 'link' at contrib/matrix/runners/perl/extract.p…
Haskell tar	tar 0.7.2.0, extract, of GHC 9.14	➖ rejects	error: Unsafe link target in tar archive: "./../escaped"
Julia Tar.jl	Tar 1.10.0 of Julia 1.13.3	➕ accepts	the expected tree
live-bootstrap untar	mescc-tools-extra a151c245e512, as live-bootstrap pins it	➕ accepts	the expected tree
live-bootstrap untar, --non-strict	mescc-tools-extra a151c245e512, as live-bootstrap pins it	➕ accepts	the expected tree

Prevalence in release tarballs¶

The table below shows how many release tarballs have the features of this test case. The default policy accepts them.

`N35-symlink-escapes.tar`	test archive, 1,536 bytes sha256 `588e06e5edf870af6822fb52fac4459d222224d4da963ee78baba86780850c60`
`N35-symlink-escapes.json`	expected result
`N35-symlink-escapes.txt`	annotated blocks
`N35-symlink-escapes.py`	generator script

ecosystem	tarballs	with it	share
Spack	37,553	0	none
nixpkgs	18,990	0	none
Guix	10,168	0	none
PyPI	10,000	2	0.02%
crates.io	5,000	0	none
RubyGems	5,000	0	none
live-bootstrap	171	0	none
total (distinct)	82,586	2	<0.01%

`N35` symlink-escapes

The case¶

The archive¶

What implementations make of it¶

Prevalence in release tarballs¶

See also¶