python
@@ -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):

@@ -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
@@ -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.