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gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback #151559

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Merged
encukou merged 4 commits into from
Jun 23, 2026
Merged

gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback #151559

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9f81791
Fix bypass
StanFromIreland Jun 10, 2026
e529baf
Update with issue number
StanFromIreland Jun 16, 2026
4a477d6
Seems we don't need Windows gating here?
StanFromIreland Jun 16, 2026
f6bc76e
Validate containment at the write loc but extract the original refere…
StanFromIreland Jun 17, 2026
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Fix bypass
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@StanFromIreland
StanFromIreland committed Jun 10, 2026
commit 9f81791353d8f1a321b22546fc5e9ef58fb0fc21
4 changes: 3 additions & 1 deletion Lib/tarfile.py
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Expand Up @@ -2784,7 +2784,9 @@ def makelink_with_filter(self, tarinfo, targetpath,
"makelink_with_filter: if filter_function is not None, "
+ "extraction_root must also not be None")
try:
filtered = filter_function(unfiltered, extraction_root)
filtered = filter_function(
unfiltered.replace(name=tarinfo.name, deep=False),
extraction_root)
except _FILTER_ERRORS as cause:
raise LinkFallbackError(tarinfo, unfiltered.name) from cause
if filtered is not None:
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27 changes: 27 additions & 0 deletions Lib/test/test_tarfile.py
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Expand Up @@ -4413,6 +4413,33 @@ def test_sneaky_hardlink_fallback(self):
self.expect_file("boom", symlink_to='../../link_here')
self.expect_file("c", symlink_to='b')

@symlink_test
def test_sneaky_hardlink_fallback_deep(self):
with ArchiveMaker() as arc:
arc.add("a/b/s", symlink_to=os.path.join("..", "escape"))
arc.add("s", hardlink_to=os.path.join("a", "b", "s"))

with self.check_context(arc.open(), 'data'):
if not os_helper.can_symlink() or sys.platform == "win32":
# See notes in test_sneaky_hardlink_fallback.
self.expect_exception(tarfile.LinkOutsideDestinationError)
else:
e = self.expect_exception(
tarfile.LinkFallbackError,
"link 's' would be extracted as a copy of "
+ "'a/b/s', which was rejected")
self.assertIsInstance(e.__cause__,
tarfile.LinkOutsideDestinationError)

for filter in 'tar', 'fully_trusted':
with self.subTest(filter), self.check_context(arc.open(), filter):
if not os_helper.can_symlink():
self.expect_file("a/b/s")
self.expect_file("s")
else:
self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
self.expect_file("s", symlink_to=os.path.join('..', 'escape'))

@symlink_test
def test_exfiltration_via_symlink(self):
# (CVE-2025-4138)
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Security/2026-06-10-13-08-19.gh-issue-111111.mL74i2.rst
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@@ -0,0 +1,3 @@
Fixed an vulnerability in the :mod:`tarfile` ``data`` and ``tar`` extraction
filters where crafted archives could create a symlink pointing outside the
destination directory. This was a bypass of :cve:`2025-4330`.