From c09dba57cfbbf74273ce44b1f48f71b46806605c Mon Sep 17 00:00:00 2001

From: "Miss Islington (bot)"

 <31488909+miss-islington@users.noreply.github.com>

Date: Thu, 10 Nov 2022 07:57:41 -0800

Subject: [PATCH] [3.9] gh-98433: Fix quadratic time idna decoding. (GH-99092)

 (GH-99222) (#99230)

There was an unnecessary quadratic loop in idna decoding. This restores

the behavior to linear.

(cherry picked from commit d315722564927c7202dd6e111dc79eaf14240b0d)

(cherry picked from commit a6f6c3a3d6f2b580f2d87885c9b8a9350ad7bf15)

Co-authored-by: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>

Co-authored-by: Gregory P. Smith <greg@krypto.org>

---

 Lib/encodings/idna.py                         | 32 +++++++++----------

 Lib/test/test_codecs.py                       |  6 ++++

 ...2-11-04-09-29-36.gh-issue-98433.l76c5G.rst |  6 ++++

 3 files changed, 27 insertions(+), 17 deletions(-)

 create mode 100644 Misc/NEWS.d/next/Security/2022-11-04-09-29-36.gh-issue-98433.l76c5G.rst

diff --git a/Lib/encodings/idna.py b/Lib/encodings/idna.py

index ea4058512fe3..bf98f513366b 100644

--- a/Lib/encodings/idna.py

+++ b/Lib/encodings/idna.py

@@ -39,23 +39,21 @@ def nameprep(label):

     # Check bidi

     RandAL = [stringprep.in_table_d1(x) for x in label]

-    for c in RandAL:

-        if c:

-            # There is a RandAL char in the string. Must perform further

-            # tests:

-            # 1) The characters in section 5.8 MUST be prohibited.

-            # This is table C.8, which was already checked

-            # 2) If a string contains any RandALCat character, the string

-            # MUST NOT contain any LCat character.

-            if any(stringprep.in_table_d2(x) for x in label):

-                raise UnicodeError("Violation of BIDI requirement 2")

-

-            # 3) If a string contains any RandALCat character, a

-            # RandALCat character MUST be the first character of the

-            # string, and a RandALCat character MUST be the last

-            # character of the string.

-            if not RandAL[0] or not RandAL[-1]:

-                raise UnicodeError("Violation of BIDI requirement 3")

+    if any(RandAL):

+        # There is a RandAL char in the string. Must perform further

+        # tests:

+        # 1) The characters in section 5.8 MUST be prohibited.

+        # This is table C.8, which was already checked

+        # 2) If a string contains any RandALCat character, the string

+        # MUST NOT contain any LCat character.

+        if any(stringprep.in_table_d2(x) for x in label):

+            raise UnicodeError("Violation of BIDI requirement 2")

+        # 3) If a string contains any RandALCat character, a

+        # RandALCat character MUST be the first character of the

+        # string, and a RandALCat character MUST be the last

+        # character of the string.

+        if not RandAL[0] or not RandAL[-1]:

+            raise UnicodeError("Violation of BIDI requirement 3")

     return label

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

index fc50e70df24b..3520cc00a1a4 100644

--- a/Lib/test/test_codecs.py

+++ b/Lib/test/test_codecs.py

@@ -1532,6 +1532,12 @@ def test_builtin_encode(self):

         self.assertEqual("pyth\xf6n.org".encode("idna"), b"xn--pythn-mua.org")

         self.assertEqual("pyth\xf6n.org.".encode("idna"), b"xn--pythn-mua.org.")

+    def test_builtin_decode_length_limit(self):

+        with self.assertRaisesRegex(UnicodeError, "too long"):

+            (b"xn--016c"+b"a"*1100).decode("idna")

+        with self.assertRaisesRegex(UnicodeError, "too long"):

+            (b"xn--016c"+b"a"*70).decode("idna")

+

     def test_stream(self):

         r = codecs.getreader("idna")(io.BytesIO(b"abc"))

         r.read(3)

diff --git a/Misc/NEWS.d/next/Security/2022-11-04-09-29-36.gh-issue-98433.l76c5G.rst b/Misc/NEWS.d/next/Security/2022-11-04-09-29-36.gh-issue-98433.l76c5G.rst

new file mode 100644

index 000000000000..5185fac2e29d

--- /dev/null

+++ b/Misc/NEWS.d/next/Security/2022-11-04-09-29-36.gh-issue-98433.l76c5G.rst

@@ -0,0 +1,6 @@

+The IDNA codec decoder used on DNS hostnames by :mod:`socket` or :mod:`asyncio`

+related name resolution functions no longer involves a quadratic algorithm.

+This prevents a potential CPU denial of service if an out-of-spec excessive

+length hostname involving bidirectional characters were decoded. Some protocols

+such as :mod:`urllib` http ``3xx`` redirects potentially allow for an attacker

+to supply such a name.