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[3.13] gh-157190: Fix tarfile `data`/`tar` filter bypass via hard link to a symlink by StanFromIreland · Pull Request #157192 · python/cpython · GitHub

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6 changes: 5 additions & 1 deletion Lib/tarfile.py
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
Original file line number Diff line number Diff line change
Expand Up @@ -2738,7 +2738,11 @@ 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 it's 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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Original file line number Diff line number Diff line change
Expand Up @@ -4452,6 +4452,24 @@ 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):
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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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
Fixed a vulnerability in the :mod:`tarfile` ``data`` and ``tar`` extraction
filters where a crafted archive using a hard link to a symbolic link could
change the permissions and modification time of a file outside the
destination directory, and expose its contents inside the extracted tree.
This addresses :cve:`2026-82049`.
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