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python39/CVE-2025-13837-plistlib-mailicious-length.patch

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From e99059d800b741504ef18693803927a0dc062be4 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 1 Dec 2025 17:28:15 +0200
Subject: [PATCH] [3.10] 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.
(cherry picked from commit 694922cf40aa3a28f898b5f5ee08b71b4922df70)
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
---
Lib/plistlib.py | 31 +++++---
Lib/test/test_plistlib.py | 37 +++++++++-
Misc/NEWS.d/next/Security/2024-05-21-22-11-31.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
Index: Python-3.9.25/Lib/plistlib.py
===================================================================
--- Python-3.9.25.orig/Lib/plistlib.py 2025-12-23 23:47:30.450823742 +0100
+++ Python-3.9.25/Lib/plistlib.py 2025-12-23 23:49:03.726727983 +0100
@@ -64,6 +64,9 @@
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):
@@ -490,12 +493,24 @@
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))
@@ -552,22 +567,16 @@
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
Index: Python-3.9.25/Lib/test/test_plistlib.py
===================================================================
--- Python-3.9.25.orig/Lib/test/test_plistlib.py 2025-12-23 23:47:31.633839488 +0100
+++ Python-3.9.25/Lib/test/test_plistlib.py 2025-12-23 23:50:05.844028198 +0100
@@ -837,8 +837,7 @@
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 = []
@@ -850,7 +849,11 @@
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
@@ -958,6 +961,34 @@
with self.assertRaises(plistlib.InvalidFileException):
plistlib.loads(b'bplist00' + data, fmt=plistlib.FMT_BINARY)
+ def test_truncated_large_data(self):
+ self.addCleanup(support.unlink, support.TESTFN)
+ def check(data):
+ with open(support.TESTFN, 'wb') as f:
+ f.write(data)
+ # buffered file
+ with open(support.TESTFN, 'rb') as f:
+ with self.assertRaises(plistlib.InvalidFileException):
+ plistlib.load(f, fmt=plistlib.FMT_BINARY)
+ # unbuffered file
+ with open(support.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))
+
class TestKeyedArchive(unittest.TestCase):
def test_keyed_archive_data(self):
Index: Python-3.9.25/Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ Python-3.9.25/Misc/NEWS.d/next/Security/2024-05-21-22-11-31.gh-issue-119342.BTFj4Z.rst 2025-12-23 23:49:03.727528792 +0100
@@ -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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