From 6816ca30af7705db691343100e696ea3d8f447d5 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Wed, 17 Jul 2019 10:13:54 -0700
Subject: [PATCH] bpo-37461: Fix infinite loop in parsing of specially crafted
 email headers (GH-14794)

* bpo-37461: Fix infinite loop in parsing of specially crafted email headers.

Some crafted email header would cause the get_parameter method to run in an
infinite loop causing a DoS attack surface when parsing those headers. This
patch fixes that by making sure the DQUOTE character is handled to prevent
going into an infinite loop.
(cherry picked from commit a4a994bd3e619cbaff97610a1cee8ffa87c672f5)

Co-authored-by: Abhilash Raj <maxking@users.noreply.github.com>
---
 Lib/email/_header_value_parser.py                          | 3 +++
 Lib/test/test_email/test__header_value_parser.py           | 7 +++++++
 .../next/Security/2019-07-16-08-11-00.bpo-37461.1Ahz7O.rst | 2 ++
 3 files changed, 12 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Security/2019-07-16-08-11-00.bpo-37461.1Ahz7O.rst

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index 64753218a36..2fc8abcbc5a 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -2475,6 +2475,9 @@ def get_parameter(value):
         while value:
             if value[0] in WSP:
                 token, value = get_fws(value)
+            elif value[0] == '"':
+                token = ValueTerminal('"', 'DQUOTE')
+                value = value[1:]
             else:
                 token, value = get_qcontent(value)
             v.append(token)
diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py
index 14d1ff36f4a..62917499996 100644
--- a/Lib/test/test_email/test__header_value_parser.py
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -2690,6 +2690,13 @@ class Test_parse_mime_parameters(TestParserMixin, TestEmailBase):
             # Defects are apparent missing *0*, and two 'out of sequence'.
             [errors.InvalidHeaderDefect]*3),
 
+        # bpo-37461: Check that we don't go into an infinite loop.
+        'extra_dquote': (
+            'r*="\'a\'\\"',
+            ' r="\\""',
+            'r*=\'a\'"',
+            [('r', '"')],
+            [errors.InvalidHeaderDefect]*2),
     }
 
 @parameterize
diff --git a/Misc/NEWS.d/next/Security/2019-07-16-08-11-00.bpo-37461.1Ahz7O.rst b/Misc/NEWS.d/next/Security/2019-07-16-08-11-00.bpo-37461.1Ahz7O.rst
new file mode 100644
index 00000000000..4bfd350c0b4
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2019-07-16-08-11-00.bpo-37461.1Ahz7O.rst
@@ -0,0 +1,2 @@
+Fix an inifite loop when parsing specially crafted email headers. Patch by
+Abhilash Raj.