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gh-157190: Follow symlinks when extracting `tarfile` hard links by StanFromIreland · Pull Request #157191 · python/cpython · GitHub

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gh-157190: Follow symlinks when extracting tarfile hard links #157191

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Merged
encukou merged 4 commits into from
Sep 10, 2026
+23 −1
Conversation 14 Commits 4 Checks 57 Files changed 2
Merged

gh-157190: Follow symlinks when extracting tarfile hard links #157191

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480ea4a
Fix symlink escape via `tarfile` hard link to symlink
StanFromIreland Sep 6, 2026
ac398e3
Drop news entry for this branch.
StanFromIreland Sep 8, 2026
027cfba
`skip_unless_hardlink` for Android/Emscriptem.
StanFromIreland Sep 8, 2026
3422b4b
Update Lib/tarfile.py
StanFromIreland Sep 9, 2026
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6 changes: 5 additions & 1 deletion Lib/tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2813,7 +2813,11 @@ def makelink_with_filter(self, tarinfo, targetpath,
if os.path.lexists(targetpath):
# Avoid FileExistsError on following os.link.
os.unlink(targetpath)
os.link(tarinfo._link_target, targetpath)
# Resolve the target so the hard link points to the file
# itself. Otherwise os.link() may duplicate a symlink to a
# shallower location, where its relative target escapes the
# destination directory. (CVE-2026-82049)
os.link(os.path.realpath(tarinfo._link_target), targetpath)
return
except symlink_exception:
keyerror_to_extracterror = True
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18 changes: 18 additions & 0 deletions Lib/test/test_tarfile.py
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Expand Up @@ -4642,6 +4642,24 @@ def test_sneaky_hardlink_fallback_deep(self):
self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
self.expect_file("s", symlink_to=os.path.join('..', 'escape'))

@symlink_test
@os_helper.skip_unless_hardlink
def test_sneaky_hardlink_relocation(self):

maurycy Sep 9, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Do we want to test also a symlink pointing to a directory?

StanFromIreland Sep 9, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I'm not sure what that would be testing, a hard link to a directory isn't possible.

maurycy Sep 9, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I meant a hard link to the symlink, where the symlink points to a directory.

Something like that:

2026-09-09T17:26:21.505759000+0200 maurycy@gimel /tmp/tarararara  % tar tvf evil.tar
drw-r--r--  0 0      0           0 Jan  1  1970 a/d/
-rw-r--r--  0 0      0           5 Jan  1  1970 a/d/f
lrw-r--r--  0 0      0           0 Jan  1  1970 a/b/s -> ../d
hrw-r--r--  0 0      0           0 Jan  1  1970 s link to a/b/s

StanFromIreland Sep 9, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

os.link() raises on a directory, so it falls through to the fallback branch, which is the path test_sneaky_hardlink_fallback_deep covers.
with ArchiveMaker() as arc:
arc.add("a/escape", content="decoy")
arc.add("a/b/s", symlink_to=os.path.join("..", "escape"))
arc.add("s", hardlink_to=os.path.join("a", "b", "s"))

for filter in 'data', 'tar':
with self.subTest(filter), self.check_context(arc.open(), filter):
self.expect_file("a/escape", content="decoy")
if os_helper.can_symlink():
self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
else:
self.expect_file("a/b/s", content="decoy")
self.expect_file("s", content="decoy")
self.assertFalse((self.destdir / "s").is_symlink())

@symlink_test
def test_exfiltration_via_symlink(self):
# (CVE-2025-4138)
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