This patch comes from upstream: http://bugs.python.org/issue16042

--- Python-2.6.8/Lib/smtplib.py

+++ Python-2.6.8/Lib/smtplib.py

@@ -57,6 +57,7 @@ from sys import stderr

 SMTP_PORT = 25

 SMTP_SSL_PORT = 465

 CRLF="\r\n"

+_MAXLINE = 8192 # more than 8 times larger than RFC 821, 4.5.3

 OLDSTYLE_AUTH = re.compile(r"auth=(.*)", re.I)

@@ -170,10 +171,14 @@ else:

         def __init__(self, sslobj):

             self.sslobj = sslobj

-        def readline(self):

+        def readline(self, size=-1):

+            if size < 0:

+                size = None

             str = ""

             chr = None

             while chr != "\n":

+                if size is not None and len(str) >= size:

+                    break

                 chr = self.sslobj.read(1)

                 if not chr: break

                 str += chr

@@ -334,11 +339,13 @@ class SMTP:

         if self.file is None:

             self.file = self.sock.makefile('rb')

         while 1:

-            line = self.file.readline()

+            line = self.file.readline(_MAXLINE + 1)

             if line == '':

                 self.close()

                 raise SMTPServerDisconnected("Connection unexpectedly closed")

-            if self.debuglevel > 0: print>>stderr, 'reply:', repr(line)

+            if self.debuglevel > 0: print >>stderr, 'reply:', repr(line)

+            if len(line) > _MAXLINE:

+                raise SMTPResponseException(500, "Line too long.")

             resp.append(line[4:].strip())

             code=line[:3]

             # Check that the error code is syntactically correct.

--- Python-2.6.8/Lib/test/test_smtplib.py

+++ Python-2.6.8/Lib/test/test_smtplib.py

@@ -273,6 +273,32 @@ class BadHELOServerTests(TestCase):

                             HOST, self.port, 'localhost', 3)

+class TooLongLineTests(TestCase):

+    respdata = '250 OK' + ('.' * smtplib._MAXLINE * 2) + '\n'

+

+    def setUp(self):

+        self.old_stdout = sys.stdout

+        self.output = StringIO.StringIO()

+        sys.stdout = self.output

+

+        self.evt = threading.Event()

+        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

+        self.sock.settimeout(15)

+        self.port = test_support.bind_port(self.sock)

+        servargs = (self.evt, self.respdata, self.sock)

+        threading.Thread(target=server, args=servargs).start()

+        self.evt.wait()

+        self.evt.clear()

+

+    def tearDown(self):

+        self.evt.wait()

+        sys.stdout = self.old_stdout

+

+    def testLineTooLong(self):

+        self.assertRaises(smtplib.SMTPResponseException, smtplib.SMTP,

+                          HOST, self.port, 'localhost', 3)

+

+

 sim_users = {'[email protected]':'John A',

              '[email protected]':'Sally B',

              '[email protected]':'Ruth C',

@@ -482,7 +508,8 @@ class SMTPSimTests(TestCase):

 def test_main(verbose=None):

     test_support.run_unittest(GeneralTests, DebuggingServerTests,

                               NonConnectingTests,

-                              BadHELOServerTests, SMTPSimTests)

+                              BadHELOServerTests, SMTPSimTests,

+                              TooLongLineTests)

 if __name__ == '__main__':

     test_main()