https://github.com/python/cpython/commit/735f25c5e3a0f74438c86468ec4dfbe219d93c91 commit: 735f25c5e3a0f74438c86468ec4dfbe219d93c91 branch: main author: Serhiy Storchaka <[email protected]> committer: encukou <[email protected]> date: 2025-01-27T14:44:00+01:00 summary:
gh-119511: Fix a potential denial of service in imaplib (#119514) The IMAP4 client could consume an arbitrary amount of memory when trying to connect 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. Co-authored-by: Gregory P. Smith <[email protected]> files: A Misc/NEWS.d/next/Security/2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst M Lib/imaplib.py M Lib/test/test_imaplib.py diff --git a/Lib/imaplib.py b/Lib/imaplib.py index e576c29e67dc0a..db708580a0abf6 100644 --- a/Lib/imaplib.py +++ b/Lib/imaplib.py @@ -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 @@ -315,7 +318,13 @@ def open(self, host='', port=IMAP4_PORT, timeout=None): def read(self, size): """Read 'size' bytes from remote.""" - return self.file.read(size) + 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) + cursize += delta + return data def readline(self): diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py index a6509fc3ba0eae..2fbf83b264d5b4 100644 --- a/Lib/test/test_imaplib.py +++ b/Lib/test/test_imaplib.py @@ -901,6 +901,20 @@ def handle(self): self.assertRaises(imaplib.IMAP4.error, self.imap_class, *server.server_address) + def test_truncated_large_literal(self): + size = 0 + class BadHandler(SimpleIMAPHandler): + def handle(self): + self._send_textline('* OK {%d}' % size) + self._send_textline('IMAP4rev1') + + for exponent in range(15, 64): + size = 1 << exponent + with self.subTest(f"size=2e{size}"): + with self.reaped_server(BadHandler) as server: + with self.assertRaises(imaplib.IMAP4.abort): + self.imap_class(*server.server_address) + @threading_helper.reap_threads def test_simple_with_statement(self): # simplest call diff --git a/Misc/NEWS.d/next/Security/2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst b/Misc/NEWS.d/next/Security/2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst new file mode 100644 index 00000000000000..f7b4031120e643 --- /dev/null +++ b/Misc/NEWS.d/next/Security/2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst @@ -0,0 +1,7 @@ +Fix a potential denial of service in the :mod:`imaplib` module. When connecting +to a malicious server, it could cause an arbitrary amount of memory to be +allocated. On many systems this is harmless as unused virtual memory is only a +mapping, but if this hit a virtual address size limit it could lead to a +:exc:`MemoryError` or other process crash. On unusual systems or builds where +all allocated memory is touched and backed by actual ram or storage it could've +consumed resources doing so until similarly crashing. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-checkins.python.org/ Member address: [email protected]
