https://github.com/python/cpython/commit/694922cf40aa3a28f898b5f5ee08b71b4922df70
commit: 694922cf40aa3a28f898b5f5ee08b71b4922df70
branch: main
author: Serhiy Storchaka <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2025-12-01T17:28:15+02:00
summary:
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.
files:
A Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst
M Lib/plistlib.py
M Lib/test/test_plistlib.py
diff --git a/Lib/plistlib.py b/Lib/plistlib.py
index 67e832db217319..655c51eea3da5d 100644
--- a/Lib/plistlib.py
+++ b/Lib/plistlib.py
@@ -73,6 +73,9 @@
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 @@ def _get_size(self, tokenL):
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 @@ def _read_object(self, ref):
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 a0c76e5dec5ebe..de2a2fd1fc34bf 100644
--- a/Lib/test/test_plistlib.py
+++ b/Lib/test/test_plistlib.py
@@ -903,8 +903,7 @@ def
test_dump_naive_datetime_with_aware_datetime_option(self):
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 @@ def decode(*objects, offset_size=1, ref_size=1):
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 @@ def test_invalid_binary(self):
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 00000000000000..04fd8faca4cf7e
--- /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.
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