diff -r 96f08a22f562 Lib/poplib.py
--- a/Lib/poplib.py	Sat Feb 23 22:21:48 2013 -0500
+++ b/Lib/poplib.py	Thu Oct 24 21:01:52 2013 +0200
@@ -40,6 +40,12 @@
 LF = b'\n'
 CRLF = CR+LF
 
+# maximal line length when calling readline(). This is to prevent
+# reading arbitrary lenght lines. RFC 1939 limits POP3 line length to
+# 512 characters, including CRLF. We have selected 2048 just to be on
+# the safe side.
+_MAXLINE = 2048
+
 
 class POP3:
 
@@ -118,7 +124,10 @@
     # Raise error_proto('-ERR EOF') if the connection is closed.
 
     def _getline(self):
-        line = self.file.readline()
+        line = self.file.readline(_MAXLINE + 1)
+        if len(line) > _MAXLINE:
+            raise error_proto('line too long')
+
         if self._debugging > 1: print('*get*', repr(line))
         if not line: raise error_proto('-ERR EOF')
         octets = len(line)
diff -r 96f08a22f562 Lib/test/test_poplib.py
--- a/Lib/test/test_poplib.py	Sat Feb 23 22:21:48 2013 -0500
+++ b/Lib/test/test_poplib.py	Thu Oct 24 21:01:52 2013 +0200
@@ -94,7 +94,7 @@
 
     def cmd_list(self, arg):
         if arg:
-            self.push('+OK %s %s' %(arg, arg))
+            self.push('+OK %s %s' % (arg, arg))
         else:
             self.push('+OK')
             asynchat.async_chat.push(self, LIST_RESP)
@@ -278,6 +278,10 @@
         foo = self.client.retr('foo')
         self.assertEqual(foo, expected)
 
+    def test_too_long_lines(self):
+        self.assertRaises(poplib.error_proto, self.client._shortcmd,
+                          'echo +%s' % (3000 * 'a'))
+
     def test_dele(self):
         self.assertOK(self.client.dele('foo'))