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2.7.18.16: tarfile streaming-mode seek loops at EOF (CVE-2026-11972) #92

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Merged
icanhasmath merged 1 commit into from
Oct 28, 2026
Merged

2.7.18.16: tarfile streaming-mode seek loops at EOF (CVE-2026-11972) #92

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4 changes: 3 additions & 1 deletion Lib/tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -556,7 +556,9 @@ def seek(self, pos=0):
if pos - self.pos >= 0:
blocks, remainder = divmod(pos - self.pos, self.bufsize)
for i in xrange(blocks):
self.read(self.bufsize)
data = self.read(self.bufsize)
if not data:
break
self.read(remainder)
else:
raise StreamError("seeking backwards is not allowed")
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16 changes: 16 additions & 0 deletions Lib/test/test_tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -592,6 +592,22 @@ def test_provoke_stream_error(self):
f = self.tar.extractfile(tarinfos[0]) # read the first member
self.assertRaises(tarfile.StreamError, f.read)

def test_getmembers_big_size(self):
# gh-151981: A loop in seek() for streaming files tried to read the
# declared number of blocks even at EOF
for format in (tarfile.GNU_FORMAT, tarfile.PAX_FORMAT):
tinfo = tarfile.TarInfo("huge-file")
tinfo.size = 1 << 64
bio = io.BytesIO()
# Write header without data
bio.write(tinfo.tobuf(format))

# Reset & try to get contents
bio.seek(0)
with tarfile.open(fileobj=bio, mode="r|") as tar:
with self.assertRaises(tarfile.ReadError):
tar.getmembers()

def test_compare_members(self):
tar1 = tarfile.open(tarname, encoding="iso8859-1")
try:
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