https://github.com/python/cpython/commit/fbc2a0ca9ac8aff6887f8ddf79b87b4510277227
commit: fbc2a0ca9ac8aff6887f8ddf79b87b4510277227
branch: 3.14
author: Miss Islington (bot) <31488909+miss-isling...@users.noreply.github.com>
committer: hugovk <1324225+hug...@users.noreply.github.com>
date: 2025-07-28T22:40:56+03:00
summary:
[3.14] gh-130577: tarfile now validates archives to ensure member offsets are
non-negative (GH-137027) (#137169)
Co-authored-by: Alexander Urieles <aeuriel...@users.noreply.github.com>
Co-authored-by: Gregory P. Smith <g...@krypto.org>
files:
A Misc/NEWS.d/next/Library/2025-07-23-00-35-29.gh-issue-130577.c7EITy.rst
M Lib/tarfile.py
M Lib/test/test_tarfile.py
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 068aa13ed70356..7f5cffc81c2aef 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1647,6 +1647,9 @@ def _block(self, count):
"""Round up a byte count by BLOCKSIZE and return it,
e.g. _block(834) => 1024.
"""
+ # Only non-negative offsets are allowed
+ if count < 0:
+ raise InvalidHeaderError("invalid offset")
blocks, remainder = divmod(count, BLOCKSIZE)
if remainder:
blocks += 1
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 7055e1ed147a9e..28914df6b010d0 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -55,6 +55,7 @@ def sha256sum(data):
zstname = os.path.join(TEMPDIR, "testtar.tar.zst")
tmpname = os.path.join(TEMPDIR, "tmp.tar")
dotlessname = os.path.join(TEMPDIR, "testtar")
+SPACE = b" "
sha256_regtype = (
"e09e4bc8b3c9d9177e77256353b36c159f5f040531bbd4b024a8f9b9196c71ce"
@@ -4602,6 +4603,161 @@ def extractall(self, ar):
ar.extractall(self.testdir, filter='fully_trusted')
+class OffsetValidationTests(unittest.TestCase):
+ tarname = tmpname
+ invalid_posix_header = (
+ # name: 100 bytes
+ tarfile.NUL * tarfile.LENGTH_NAME
+ # mode, space, null terminator: 8 bytes
+ + b"000755" + SPACE + tarfile.NUL
+ # uid, space, null terminator: 8 bytes
+ + b"000001" + SPACE + tarfile.NUL
+ # gid, space, null terminator: 8 bytes
+ + b"000001" + SPACE + tarfile.NUL
+ # size, space: 12 bytes
+ + b"\xff" * 11 + SPACE
+ # mtime, space: 12 bytes
+ + tarfile.NUL * 11 + SPACE
+ # chksum: 8 bytes
+ + b"0011407" + tarfile.NUL
+ # type: 1 byte
+ + tarfile.REGTYPE
+ # linkname: 100 bytes
+ + tarfile.NUL * tarfile.LENGTH_LINK
+ # magic: 6 bytes, version: 2 bytes
+ + tarfile.POSIX_MAGIC
+ # uname: 32 bytes
+ + tarfile.NUL * 32
+ # gname: 32 bytes
+ + tarfile.NUL * 32
+ # devmajor, space, null terminator: 8 bytes
+ + tarfile.NUL * 6 + SPACE + tarfile.NUL
+ # devminor, space, null terminator: 8 bytes
+ + tarfile.NUL * 6 + SPACE + tarfile.NUL
+ # prefix: 155 bytes
+ + tarfile.NUL * tarfile.LENGTH_PREFIX
+ # padding: 12 bytes
+ + tarfile.NUL * 12
+ )
+ invalid_gnu_header = (
+ # name: 100 bytes
+ tarfile.NUL * tarfile.LENGTH_NAME
+ # mode, null terminator: 8 bytes
+ + b"0000755" + tarfile.NUL
+ # uid, null terminator: 8 bytes
+ + b"0000001" + tarfile.NUL
+ # gid, space, null terminator: 8 bytes
+ + b"0000001" + tarfile.NUL
+ # size, space: 12 bytes
+ + b"\xff" * 11 + SPACE
+ # mtime, space: 12 bytes
+ + tarfile.NUL * 11 + SPACE
+ # chksum: 8 bytes
+ + b"0011327" + tarfile.NUL
+ # type: 1 byte
+ + tarfile.REGTYPE
+ # linkname: 100 bytes
+ + tarfile.NUL * tarfile.LENGTH_LINK
+ # magic: 8 bytes
+ + tarfile.GNU_MAGIC
+ # uname: 32 bytes
+ + tarfile.NUL * 32
+ # gname: 32 bytes
+ + tarfile.NUL * 32
+ # devmajor, null terminator: 8 bytes
+ + tarfile.NUL * 8
+ # devminor, null terminator: 8 bytes
+ + tarfile.NUL * 8
+ # padding: 167 bytes
+ + tarfile.NUL * 167
+ )
+ invalid_v7_header = (
+ # name: 100 bytes
+ tarfile.NUL * tarfile.LENGTH_NAME
+ # mode, space, null terminator: 8 bytes
+ + b"000755" + SPACE + tarfile.NUL
+ # uid, space, null terminator: 8 bytes
+ + b"000001" + SPACE + tarfile.NUL
+ # gid, space, null terminator: 8 bytes
+ + b"000001" + SPACE + tarfile.NUL
+ # size, space: 12 bytes
+ + b"\xff" * 11 + SPACE
+ # mtime, space: 12 bytes
+ + tarfile.NUL * 11 + SPACE
+ # chksum: 8 bytes
+ + b"0010070" + tarfile.NUL
+ # type: 1 byte
+ + tarfile.REGTYPE
+ # linkname: 100 bytes
+ + tarfile.NUL * tarfile.LENGTH_LINK
+ # padding: 255 bytes
+ + tarfile.NUL * 255
+ )
+ valid_gnu_header = tarfile.TarInfo("filename").tobuf(tarfile.GNU_FORMAT)
+ data_block = b"\xff" * tarfile.BLOCKSIZE
+
+ def _write_buffer(self, buffer):
+ with open(self.tarname, "wb") as f:
+ f.write(buffer)
+
+ def _get_members(self, ignore_zeros=None):
+ with open(self.tarname, "rb") as f:
+ with tarfile.open(
+ mode="r", fileobj=f, ignore_zeros=ignore_zeros
+ ) as tar:
+ return tar.getmembers()
+
+ def _assert_raises_read_error_exception(self):
+ with self.assertRaisesRegex(
+ tarfile.ReadError, "file could not be opened successfully"
+ ):
+ self._get_members()
+
+ def test_invalid_offset_header_validations(self):
+ for tar_format, invalid_header in (
+ ("posix", self.invalid_posix_header),
+ ("gnu", self.invalid_gnu_header),
+ ("v7", self.invalid_v7_header),
+ ):
+ with self.subTest(format=tar_format):
+ self._write_buffer(invalid_header)
+ self._assert_raises_read_error_exception()
+
+ def test_early_stop_at_invalid_offset_header(self):
+ buffer = self.valid_gnu_header + self.invalid_gnu_header +
self.valid_gnu_header
+ self._write_buffer(buffer)
+ members = self._get_members()
+ self.assertEqual(len(members), 1)
+ self.assertEqual(members[0].name, "filename")
+ self.assertEqual(members[0].offset, 0)
+
+ def test_ignore_invalid_archive(self):
+ # 3 invalid headers with their respective data
+ buffer = (self.invalid_gnu_header + self.data_block) * 3
+ self._write_buffer(buffer)
+ members = self._get_members(ignore_zeros=True)
+ self.assertEqual(len(members), 0)
+
+ def test_ignore_invalid_offset_headers(self):
+ for first_block, second_block, expected_offset in (
+ (
+ (self.valid_gnu_header),
+ (self.invalid_gnu_header + self.data_block),
+ 0,
+ ),
+ (
+ (self.invalid_gnu_header + self.data_block),
+ (self.valid_gnu_header),
+ 1024,
+ ),
+ ):
+ self._write_buffer(first_block + second_block)
+ members = self._get_members(ignore_zeros=True)
+ self.assertEqual(len(members), 1)
+ self.assertEqual(members[0].name, "filename")
+ self.assertEqual(members[0].offset, expected_offset)
+
+
def setUpModule():
os_helper.unlink(TEMPDIR)
os.makedirs(TEMPDIR)
diff --git
a/Misc/NEWS.d/next/Library/2025-07-23-00-35-29.gh-issue-130577.c7EITy.rst
b/Misc/NEWS.d/next/Library/2025-07-23-00-35-29.gh-issue-130577.c7EITy.rst
new file mode 100644
index 00000000000000..342cabbc865dc4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-07-23-00-35-29.gh-issue-130577.c7EITy.rst
@@ -0,0 +1,3 @@
+:mod:`tarfile` now validates archives to ensure member offsets are
+non-negative. (Contributed by Alexander Enrique Urieles Nieto in
+:gh:`130577`.)
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