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[3.8] gh-99889: Fix directory traversal security flaw in uu.decode() (GH-104096) by miss-islington · Pull Request #104332 · python/cpython · GitHub

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[3.8] gh-99889: Fix directory traversal security flaw in uu.decode() (GH-104096) #104332

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Merged
ambv merged 1 commit into from
May 22, 2023
+38 −1
Conversation 0 Commits 1 Checks 0 Files changed 3
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[3.8] gh-99889: Fix directory traversal security flaw in uu.decode() (GH-104096) #104332

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28 changes: 28 additions & 0 deletions Lib/test/test_uu.py
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Original file line number Diff line number Diff line change
Expand Up @@ -145,6 +145,34 @@ def test_newlines_escaped(self):
uu.encode(inp, out, filename)
self.assertIn(safefilename, out.getvalue())

def test_no_directory_traversal(self):
relative_bad = b"""\
begin 644 ../../../../../../../../tmp/test1
$86)C"@``
`
end
"""
with self.assertRaisesRegex(uu.Error, 'directory'):
uu.decode(io.BytesIO(relative_bad))
if os.altsep:
relative_bad_bs = relative_bad.replace(b'/', b'\\')
with self.assertRaisesRegex(uu.Error, 'directory'):
uu.decode(io.BytesIO(relative_bad_bs))

absolute_bad = b"""\
begin 644 /tmp/test2
$86)C"@``
`
end
"""
with self.assertRaisesRegex(uu.Error, 'directory'):
uu.decode(io.BytesIO(absolute_bad))
if os.altsep:
absolute_bad_bs = absolute_bad.replace(b'/', b'\\')
with self.assertRaisesRegex(uu.Error, 'directory'):
uu.decode(io.BytesIO(absolute_bad_bs))


class UUStdIOTest(unittest.TestCase):

def setUp(self):
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9 changes: 8 additions & 1 deletion Lib/uu.py
100755 → 100644
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,14 @@ def decode(in_file, out_file=None, mode=None, quiet=False):
# If the filename isn't ASCII, what's up with that?!?
out_file = hdrfields[2].rstrip(b' \t\r\n\f').decode("ascii")
if os.path.exists(out_file):
raise Error('Cannot overwrite existing file: %s' % out_file)
raise Error(f'Cannot overwrite existing file: {out_file}')
if (out_file.startswith(os.sep) or
f'..{os.sep}' in out_file or (
os.altsep and
(out_file.startswith(os.altsep) or
f'..{os.altsep}' in out_file))
):
raise Error(f'Refusing to write to {out_file} due to directory traversal')
if mode is None:
mode = int(hdrfields[1], 8)
#
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Security/2023-05-02-17-56-32.gh-issue-99889.l664SU.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fixed a security in flaw in :func:`uu.decode` that could allow for
directory traversal based on the input if no ``out_file`` was specified.
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