From f602e097f64860915e3c32c63fba58a834d2086b Mon Sep 17 00:00:00 2001
From: Abhilash Raj <maxking@users.noreply.github.com>
Date: Wed, 17 Jul 2019 09:44:27 -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 f42cde203cef9e9..c27352f64a48b2c 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -2366,6 +2366,9 @@ 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 676732bb3d02616..a2c900fa7fd2c99 100644
--- a/Lib/test/test_email/test__header_value_parser.py
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -2601,6 +2601,13 @@ def mime_parameters_as_value(self,
             # 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 000000000000000..4bfd350c0b404eb
--- /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.