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[3.11] gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback (GH-151559) #152001

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Merged
pablogsal merged 2 commits into from
Jun 27, 2026
Merged

[3.11] gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback (GH-151559) #152001

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gh-151558: Fix symlink escape via `tarfile` hardlink-extraction fallb…
StanFromIreland Jun 23, 2026
9fe3c36
Can't use `:cve:` on 3.11
StanFromIreland Jun 23, 2026
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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 @@ -2663,6 +2663,9 @@ 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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Original file line number Diff line number Diff line change
Expand Up @@ -3998,6 +3998,30 @@ 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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Original file line number Diff line number Diff line change
@@ -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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