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gh-119511: Fix a potential denial of service in imaplib #119514

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Merged
encukou merged 6 commits into from
Jan 27, 2025
Merged

gh-119511: Fix a potential denial of service in imaplib #119514

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6322049
gh-119511: Fix OOM vulnerability in imaplib
serhiy-storchaka May 24, 2024
284a553
Update Lib/imaplib.py
serhiy-storchaka May 30, 2024
d7abc31
modernize the test, expand the NEWS entry.
gpshead Jan 20, 2025
1c74be4
Merge branch 'main' into imaplib-oom
gpshead Jan 20, 2025
d71a7ee
use a subTest for sizes
gpshead Jan 20, 2025
f6a41df
wording tweak.
gpshead Jan 20, 2025
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gh-119511: Fix OOM vulnerability in imaplib 
The IMAP4 client could consume an arbitrary amount of memory when trying
to connent to a malicious server, because it read a "literal" data with a
single read(size) call, and BufferedReader.read() allocates the bytes
object of the specified size before reading. Now the IMAP4 client reads data
by chunks, therefore the amount of used memory is limited by the
amount of the data actually been sent by the server.
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@serhiy-storchaka
serhiy-storchaka committed May 24, 2024
commit 6322049d1285f652e5a33144271200c1fe0c3746
10 changes: 10 additions & 0 deletions Lib/imaplib.py
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Expand Up @@ -52,6 +52,9 @@
# search command can be quite large, so we now use 1M.
_MAXLINE = 1000000

# Data larger than this will be read in chunks, to prevent extreme
# overallocation.
_SAFE_BUF_SIZE = 1 << 20

# Commands

Expand Down Expand Up @@ -315,6 +318,13 @@ def open(self, host='', port=IMAP4_PORT, timeout=None):

def read(self, size):
"""Read 'size' bytes from remote."""
cursize = min(size, _SAFE_BUF_SIZE)
data = self.file.read(cursize)
while cursize < size and len(data) == cursize:
delta = min(cursize, size - cursize)
data += self.file.read(delta)
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cursize += delta
return data
return self.file.read(size)

@keepworking keepworking May 30, 2024

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I think you've missed erasing this part.

@serhiy-storchaka serhiy-storchaka May 30, 2024

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Good catch!

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12 changes: 12 additions & 0 deletions Lib/test/test_imaplib.py
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Expand Up @@ -907,6 +907,18 @@ def handle(self):
self.assertRaises(imaplib.IMAP4.error,
self.imap_class, *server.server_address)

def test_truncated_large_literal(self):
class BadHandler(SimpleIMAPHandler):
def handle(self):
self._send_textline('* OK {%d}' % size)
self._send_textline('IMAP4rev1')

for w in range(15, 64):
size = 1 << w
with self.reaped_server(BadHandler) as server:
self.assertRaises(imaplib.IMAP4.abort,
self.imap_class, *server.server_address)

@threading_helper.reap_threads
def test_simple_with_statement(self):
# simplest call
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Security/2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst
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@@ -0,0 +1,2 @@
Fix a vulnerability in the :mod:`imaplib` module, when connecting to a
malicious server could cause an arbitrary amount of memory to be consumed.