From 694922cf40aa3a28f898b5f5ee08b71b4922df70 Mon Sep 17 00:00:00 2001 From: Serhiy Storchaka Date: Mon, 1 Dec 2025 17:28:15 +0200 Subject: [PATCH] gh-119342: Fix a potential denial of service in plistlib (GH-119343) Reading a specially prepared small Plist file could cause OOM because file's read(n) preallocates a bytes object for reading the specified amount of data. Now plistlib reads large data by chunks, therefore the upper limit of consumed memory is proportional to the size of the input file. --- Lib/plistlib.py | 31 ++++++++++------ Lib/test/test_plistlib.py | 37 +++++++++++++++++-- ...-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst | 5 +++ 3 files changed, 59 insertions(+), 14 deletions(-) create mode 100644 Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst diff --git a/Lib/plistlib.py b/Lib/plistlib.py index 67e832db2173..655c51eea3da 100644 --- a/Lib/plistlib.py +++ b/Lib/plistlib.py @@ -73,6 +73,9 @@ from xml.parsers.expat import ParserCreate PlistFormat = enum.Enum('PlistFormat', 'FMT_XML FMT_BINARY', module=__name__) globals().update(PlistFormat.__members__) +# Data larger than this will be read in chunks, to prevent extreme +# overallocation. +_MIN_READ_BUF_SIZE = 1 << 20 class UID: def __init__(self, data): @@ -508,12 +511,24 @@ class _BinaryPlistParser: return tokenL + def _read(self, size): + cursize = min(size, _MIN_READ_BUF_SIZE) + data = self._fp.read(cursize) + while True: + if len(data) != cursize: + raise InvalidFileException + if cursize == size: + return data + delta = min(cursize, size - cursize) + data += self._fp.read(delta) + cursize += delta + def _read_ints(self, n, size): - data = self._fp.read(size * n) + data = self._read(size * n) if size in _BINARY_FORMAT: return struct.unpack(f'>{n}{_BINARY_FORMAT[size]}', data) else: - if not size or len(data) != size * n: + if not size: raise InvalidFileException() return tuple(int.from_bytes(data[i: i + size], 'big') for i in range(0, size * n, size)) @@ -573,22 +588,16 @@ class _BinaryPlistParser: elif tokenH == 0x40: # data s = self._get_size(tokenL) - result = self._fp.read(s) - if len(result) != s: - raise InvalidFileException() + result = self._read(s) elif tokenH == 0x50: # ascii string s = self._get_size(tokenL) - data = self._fp.read(s) - if len(data) != s: - raise InvalidFileException() + data = self._read(s) result = data.decode('ascii') elif tokenH == 0x60: # unicode string s = self._get_size(tokenL) * 2 - data = self._fp.read(s) - if len(data) != s: - raise InvalidFileException() + data = self._read(s) result = data.decode('utf-16be') elif tokenH == 0x80: # UID diff --git a/Lib/test/test_plistlib.py b/Lib/test/test_plistlib.py index a0c76e5dec5e..de2a2fd1fc34 100644 --- a/Lib/test/test_plistlib.py +++ b/Lib/test/test_plistlib.py @@ -903,8 +903,7 @@ class TestPlistlib(unittest.TestCase): class TestBinaryPlistlib(unittest.TestCase): - @staticmethod - def decode(*objects, offset_size=1, ref_size=1): + def build(self, *objects, offset_size=1, ref_size=1): data = [b'bplist00'] offset = 8 offsets = [] @@ -916,7 +915,11 @@ class TestBinaryPlistlib(unittest.TestCase): len(objects), 0, offset) data.extend(offsets) data.append(tail) - return plistlib.loads(b''.join(data), fmt=plistlib.FMT_BINARY) + return b''.join(data) + + def decode(self, *objects, offset_size=1, ref_size=1): + data = self.build(*objects, offset_size=offset_size, ref_size=ref_size) + return plistlib.loads(data, fmt=plistlib.FMT_BINARY) def test_nonstandard_refs_size(self): # Issue #21538: Refs and offsets are 24-bit integers @@ -1024,6 +1027,34 @@ class TestBinaryPlistlib(unittest.TestCase): with self.assertRaises(plistlib.InvalidFileException): plistlib.loads(b'bplist00' + data, fmt=plistlib.FMT_BINARY) + def test_truncated_large_data(self): + self.addCleanup(os_helper.unlink, os_helper.TESTFN) + def check(data): + with open(os_helper.TESTFN, 'wb') as f: + f.write(data) + # buffered file + with open(os_helper.TESTFN, 'rb') as f: + with self.assertRaises(plistlib.InvalidFileException): + plistlib.load(f, fmt=plistlib.FMT_BINARY) + # unbuffered file + with open(os_helper.TESTFN, 'rb', buffering=0) as f: + with self.assertRaises(plistlib.InvalidFileException): + plistlib.load(f, fmt=plistlib.FMT_BINARY) + for w in range(20, 64): + s = 1 << w + # data + check(self.build(b'\x4f\x13' + s.to_bytes(8, 'big'))) + # ascii string + check(self.build(b'\x5f\x13' + s.to_bytes(8, 'big'))) + # unicode string + check(self.build(b'\x6f\x13' + s.to_bytes(8, 'big'))) + # array + check(self.build(b'\xaf\x13' + s.to_bytes(8, 'big'))) + # dict + check(self.build(b'\xdf\x13' + s.to_bytes(8, 'big'))) + # number of objects + check(b'bplist00' + struct.pack('>6xBBQQQ', 1, 1, s, 0, 8)) + def test_load_aware_datetime(self): data = (b'bplist003B\x04>\xd0d\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00' b'\x01\x01\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00' diff --git a/Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst b/Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst new file mode 100644 index 000000000000..04fd8faca4cf --- /dev/null +++ b/Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst @@ -0,0 +1,5 @@ +Fix a potential memory denial of service in the :mod:`plistlib` module. +When reading a Plist file received from untrusted source, it could cause +an arbitrary amount of memory to be allocated. +This could have led to symptoms including a :exc:`MemoryError`, swapping, out +of memory (OOM) killed processes or containers, or even system crashes. -- 2.47.3