diff --git a/Lib/difflib.py b/Lib/difflib.py

index 1c6fbdbedcb7..788a92df3f89 100644

--- a/Lib/difflib.py

+++ b/Lib/difflib.py

@@ -1103,7 +1103,7 @@ def _qformat(self, aline, bline, atags, btags):

 import re

-def IS_LINE_JUNK(line, pat=re.compile(r"\s*#?\s*$").match):

+def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match):

     r"""

     Return 1 for ignorable line: iff `line` is blank or contains a single '#'.

diff --git a/Lib/poplib.py b/Lib/poplib.py

index b91e5f72d2ca..a238510b38fc 100644

--- a/Lib/poplib.py

+++ b/Lib/poplib.py

@@ -274,7 +274,7 @@ def rpop(self, user):

         return self._shortcmd('RPOP %s' % user)

-    timestamp = re.compile(r'\+OK.*(<[^>]+>)')

+    timestamp = re.compile(br'\+OK.[^<]*(<.*>)')

     def apop(self, user, secret):

         """Authorisation

diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py

index 35f2c36ca70a..d8277b79b880 100644

--- a/Lib/test/test_difflib.py

+++ b/Lib/test/test_difflib.py

@@ -269,13 +269,33 @@ def test_range_format_context(self):

         self.assertEqual(fmt(3,6), '4,6')

         self.assertEqual(fmt(0,0), '0')

+class TestJunkAPIs(unittest.TestCase):

+    def test_is_line_junk_true(self):

+        for line in ['#', '  ', ' #', '# ', ' # ', '']:

+            self.assertTrue(difflib.IS_LINE_JUNK(line), repr(line))

+

+    def test_is_line_junk_false(self):

+        for line in ['##', ' ##', '## ', 'abc ', 'abc #', 'Mr. Moose is up!']:

+            self.assertFalse(difflib.IS_LINE_JUNK(line), repr(line))

+

+    def test_is_line_junk_REDOS(self):

+        evil_input = ('\t' * 1000000) + '##'

+        self.assertFalse(difflib.IS_LINE_JUNK(evil_input))

+

+    def test_is_character_junk_true(self):

+        for char in [' ', '\t']:

+            self.assertTrue(difflib.IS_CHARACTER_JUNK(char), repr(char))

+

+    def test_is_character_junk_false(self):

+        for char in ['a', '#', '\n', '\f', '\r', '\v']:

+            self.assertFalse(difflib.IS_CHARACTER_JUNK(char), repr(char))

 def test_main():

     difflib.HtmlDiff._default_prefix = 0

     Doctests = doctest.DocTestSuite(difflib)

     run_unittest(

         TestWithAscii, TestAutojunk, TestSFpatches, TestSFbugs,

-        TestOutputFormat, Doctests)

+        TestOutputFormat, TestJunkAPIs)

 if __name__ == '__main__':

     test_main()

diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py

index 23d688724b95..d2143759ba66 100644

--- a/Lib/test/test_poplib.py

+++ b/Lib/test/test_poplib.py

@@ -211,6 +211,16 @@ def test_noop(self):

     def test_rpop(self):

         self.assertOK(self.client.rpop('foo'))

+    def test_apop_REDOS(self):

+        # Replace welcome with very long evil welcome.

+        # NB The upper bound on welcome length is currently 2048.

+        # At this length, evil input makes each apop call take

+        # on the order of milliseconds instead of microseconds.

+        evil_welcome = b'+OK' + (b'<' * 1000000)

+        with test_support.swap_attr(self.client, 'welcome', evil_welcome):

+            # The evil welcome is invalid, so apop should throw.

+            self.assertRaises(poplib.error_proto, self.client.apop, 'a', 'kb')

+

     def test_top(self):

         expected =  ('+OK 116 bytes',

                      ['From: postmaster@python.org', 'Content-Type: text/plain',