[Python-checkins] bpo-37461: Fix infinite loop in parsing of specially crafted email headers (GH-14794) (GH-14817)

[Ned Deily]

https://github.com/python/cpython/commit/1789bbdd3e03023951a39933ef12dee0a03be616
commit: 1789bbdd3e03023951a39933ef12dee0a03be616
branch: 3.6
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Ned Deily <nad at python.org>
date: 2019-08-01T12:36:46-04:00
summary:

bpo-37461: Fix infinite loop in parsing of specially crafted email headers (GH-14794) (GH-14817)

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 at users.noreply.github.com>

files:
A Misc/NEWS.d/next/Security/2019-07-16-08-11-00.bpo-37461.1Ahz7O.rst
M Lib/email/_header_value_parser.py
M Lib/test/test_email/test__header_value_parser.py

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index e3c343dffb42..737951e4b1b1 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 676732bb3d02..a2c900fa7fd2 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 000000000000..4bfd350c0b40
--- /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.