From 817564849e59ac5ccc4493b3596bccbb8cbfd375 Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Wed, 19 Feb 2025 14:30:32 +0100 Subject: [PATCH] [3.10] gh-119511: Fix a potential denial of service in imaplib (GH-119514) (#129358) MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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. (cherry picked from commit 735f25c5e3a0f74438c86468ec4dfbe219d93c91) Co-authored-by: Serhiy Storchaka Co-authored-by: Gregory P. Smith Co-authored-by: Łukasz Langa --- Lib/imaplib.py | 11 ++++++++++- Lib/test/test_imaplib.py | 14 ++++++++++++++ .../2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst | 7 +++++++ 3 files changed, 31 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Security/2024-05-24-21-00-52.gh-issue-119511.jKrXQ8.rst diff --git a/Lib/imaplib.py b/Lib/imaplib.py index 73184396d894..54122f985b9a 100644 --- a/Lib/imaplib.py +++ b/Lib/imaplib.py @@ -52,6 +52,9 @@ AllowedVersions = ('IMAP4REV1', 'IMAP4') # Most recent first # 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 @@ class IMAP4: 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 b5c78a5d49c5..f8177077439d 100644 --- a/Lib/test/test_imaplib.py +++ b/Lib/test/test_imaplib.py @@ -908,6 +908,20 @@ class ThreadedNetworkedTests(unittest.TestCase): 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 000000000000..f7b4031120e6 --- /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. -- 2.47.3