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[3.12] gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback (GH-151559) #152000

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Merged
Yhg1s merged 1 commit into from
Aug 4, 2026
Merged

[3.12] gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback (GH-151559) #152000

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gh-151558: Fix symlink escape via tarfile hardlink-extraction fallb… 
…ack (GH-151559)

(cherry picked from commit 27dd970)

Co-authored-by: Stan Ulbrych <stan@python.org>
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@StanFromIreland @miss-islington
StanFromIreland authored and miss-islington committed Jun 23, 2026
commit d0ba16dce6df2f68e8968699d5c247eddeef9960
3 changes: 3 additions & 0 deletions Lib/tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2677,6 +2677,9 @@ def makelink_with_filter(self, tarinfo, targetpath,
"makelink_with_filter: if filter_function is not None, "
+ "extraction_root must also not be None")
try:
filter_function(
unfiltered.replace(name=tarinfo.name, deep=False),
extraction_root)
filtered = filter_function(unfiltered, extraction_root)
except _FILTER_ERRORS as cause:
raise LinkFallbackError(tarinfo, unfiltered.name) from cause
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24 changes: 24 additions & 0 deletions Lib/test/test_tarfile.py
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Expand Up @@ -4182,6 +4182,30 @@ 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):
# (CVE-2026-11940)
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'):
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/")
self.expect_file("a/b/")
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-151558.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`.
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