From 17358fb35fb7217423d4c4877ccb6d1a3a40b1c3 Mon Sep 17 00:00:00 2001
From: Sarah Boyce <42296566+sarahboyce@users.noreply.github.com>
Date: Wed, 26 Jun 2024 12:11:54 +0200
Subject: [PATCH] [4.2.x] Fixed CVE-2024-39614 -- Mitigated potential DoS in
 get_supported_language_variant().

Language codes are now parsed with a maximum length limit of 500 chars.

Thanks to MProgrammer for the report.

CVE: CVE-2024-39614

Upstream-Status: Backport [https://github.com/django/django/commit/17358fb35fb7217423d4c4877ccb6d1a3a40b1c3]

Signed-off-by: Soumya Sambu <soumya.sambu@windriver.com>
---
 django/utils/translation/trans_real.py | 24 ++++++++++++++++++++----
 docs/ref/utils.txt                     | 10 ++++++++++
 tests/i18n/tests.py                    | 11 +++++++++++
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/django/utils/translation/trans_real.py b/django/utils/translation/trans_real.py
index 7f658cf..56b4ef1 100644
--- a/django/utils/translation/trans_real.py
+++ b/django/utils/translation/trans_real.py
@@ -30,8 +30,10 @@ _default = None
 CONTEXT_SEPARATOR = "\x04"

 # Maximum number of characters that will be parsed from the Accept-Language
-# header to prevent possible denial of service or memory exhaustion attacks.
-ACCEPT_LANGUAGE_HEADER_MAX_LENGTH = 500
+# header or cookie to prevent possible denial of service or memory exhaustion
+# attacks. About 10x longer than the longest value shown on MDN’s
+# Accept-Language page.
+LANGUAGE_CODE_MAX_LENGTH = 500

 # Format of Accept-Language header values. From RFC 2616, section 14.4 and 3.9
 # and RFC 3066, section 2.1
@@ -472,11 +474,25 @@ def get_supported_language_variant(lang_code, strict=False):
     If `strict` is False (the default), look for a country-specific variant
     when neither the language code nor its generic variant is found.

+    The language code is truncated to a maximum length to avoid potential
+    denial of service attacks.
+
     lru_cache should have a maxsize to prevent from memory exhaustion attacks,
     as the provided language codes are taken from the HTTP request. See also
     <https://www.djangoproject.com/weblog/2007/oct/26/security-fix/>.
     """
     if lang_code:
+        # Truncate the language code to a maximum length to avoid potential
+        # denial of service attacks.
+        if len(lang_code) > LANGUAGE_CODE_MAX_LENGTH:
+            if (
+                not strict
+                and (index := lang_code.rfind("-", 0, LANGUAGE_CODE_MAX_LENGTH)) > 0
+            ):
+                # There is a generic variant under the maximum length accepted length.
+                lang_code = lang_code[:index]
+            else:
+                raise ValueError("'lang_code' exceeds the maximum accepted length")
         # If 'fr-ca' is not supported, try special fallback or language-only 'fr'.
         possible_lang_codes = [lang_code]
         try:
@@ -598,12 +614,12 @@ def parse_accept_lang_header(lang_string):
     `functools.lru_cache()` to avoid repetitive parsing of common header values.
     """
     # If the header value doesn't exceed the maximum allowed length, parse it.
-    if len(lang_string) <= ACCEPT_LANGUAGE_HEADER_MAX_LENGTH:
+    if len(lang_string) <= LANGUAGE_CODE_MAX_LENGTH:
         return _parse_accept_lang_header(lang_string)

     # If there is at least one comma in the value, parse up to the last comma,
     # skipping any truncated parts at the end of the header value.
-    index = lang_string.rfind(",", 0, ACCEPT_LANGUAGE_HEADER_MAX_LENGTH)
+    index = lang_string.rfind(",", 0, LANGUAGE_CODE_MAX_LENGTH)
     if index > 0:
         return _parse_accept_lang_header(lang_string[:index])

diff --git a/docs/ref/utils.txt b/docs/ref/utils.txt
index 390f167..63a56e5 100644
--- a/docs/ref/utils.txt
+++ b/docs/ref/utils.txt
@@ -1142,6 +1142,11 @@ functions without the ``u``.
     ``lang_code`` is ``'es-ar'`` and ``'es'`` is in :setting:`LANGUAGES` but
     ``'es-ar'`` isn't.

+    ``lang_code`` has a maximum accepted length of 500 characters. A
+    :exc:`ValueError` is raised if ``lang_code`` exceeds this limit and
+    ``strict`` is ``True``, or if there is no generic variant and ``strict``
+    is ``False``.
+
     If ``strict`` is ``False`` (the default), a country-specific variant may
     be returned when neither the language code nor its generic variant is found.
     For example, if only ``'es-co'`` is in :setting:`LANGUAGES`, that's
@@ -1150,6 +1155,11 @@ functions without the ``u``.

     Raises :exc:`LookupError` if nothing is found.

+    .. versionchanged:: 4.2.14
+
+        In older versions, ``lang_code`` values over 500 characters were
+        processed without raising a :exc:`ValueError`.
+
 .. function:: to_locale(language)

     Turns a language name (en-us) into a locale name (en_US).
diff --git a/tests/i18n/tests.py b/tests/i18n/tests.py
index 6efc3a5..0e93395 100644
--- a/tests/i18n/tests.py
+++ b/tests/i18n/tests.py
@@ -39,6 +39,7 @@ from django.utils.translation import (
 from django.utils.translation.reloader import (
     translation_file_changed, watch_for_translation_changes,
 )
+from django.utils.translation.trans_real import LANGUAGE_CODE_MAX_LENGTH

 from .forms import CompanyForm, I18nForm, SelectDateForm
 from .models import Company, TestModel
@@ -1462,6 +1463,16 @@ class MiscTests(SimpleTestCase):
             g('xyz')
         with self.assertRaises(LookupError):
             g('xy-zz')
+        msg = "'lang_code' exceeds the maximum accepted length"
+        with self.assertRaises(LookupError):
+            g("x" * LANGUAGE_CODE_MAX_LENGTH)
+        with self.assertRaisesMessage(ValueError, msg):
+            g("x" * (LANGUAGE_CODE_MAX_LENGTH + 1))
+        # 167 * 3 = 501 which is LANGUAGE_CODE_MAX_LENGTH + 1.
+        self.assertEqual(g("en-" * 167), "en")
+        with self.assertRaisesMessage(ValueError, msg):
+            g("en-" * 167, strict=True)
+        self.assertEqual(g("en-" * 30000), "en")  # catastrophic test

     def test_get_supported_language_variant_null(self):
         g = trans_null.get_supported_language_variant
--
2.40.0
