From 225412b13f66a76a7222d7719777e6162638faa3 Mon Sep 17 00:00:00 2001
From: Sam Bull <git@sambull.org>
Date: Sat, 3 Jan 2026 00:02:45 +0000
Subject: [PATCH] Reject non-ascii characters in some headers (#11886) (#11902)

(cherry picked from commit 5affd64f86d28a16a8f8e6fea2d217c99bf7831f)

CVE: CVE-2025-69224
Upstream-Status: Backport [https://github.com/aio-libs/aiohttp/commit/32677f2adfd907420c078dda6b79225c6f4ebce0]
Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>
---
 aiohttp/_http_parser.pyx  |  6 +++---
 aiohttp/http_parser.py    |  8 ++++++--
 tests/test_http_parser.py | 16 +++++++++++++++-
 3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/aiohttp/_http_parser.pyx b/aiohttp/_http_parser.pyx
index 16893f0..23f1dd1 100644
--- a/aiohttp/_http_parser.pyx
+++ b/aiohttp/_http_parser.pyx
@@ -421,7 +421,8 @@ cdef class HttpParser:
         headers = CIMultiDictProxy(CIMultiDict(self._headers))
 
         if self._cparser.type == cparser.HTTP_REQUEST:
-            allowed = upgrade and headers.get("upgrade", "").lower() in ALLOWED_UPGRADES
+            h_upg = headers.get("upgrade", "")
+            allowed = upgrade and h_upg.isascii() and h_upg.lower() in ALLOWED_UPGRADES
             if allowed or self._cparser.method == cparser.HTTP_CONNECT:
                 self._upgraded = True
         else:
@@ -436,8 +437,7 @@ cdef class HttpParser:
         enc = self._content_encoding
         if enc is not None:
             self._content_encoding = None
-            enc = enc.lower()
-            if enc in ('gzip', 'deflate', 'br'):
+            if enc.isascii() and enc.lower() in {"gzip", "deflate", "br"}:
                 encoding = enc
 
         if self._cparser.type == cparser.HTTP_REQUEST:
diff --git a/aiohttp/http_parser.py b/aiohttp/http_parser.py
index 9f864b2..bc8f7da 100644
--- a/aiohttp/http_parser.py
+++ b/aiohttp/http_parser.py
@@ -232,7 +232,9 @@ class HeadersParser:
 
 def _is_supported_upgrade(headers: CIMultiDictProxy[str]) -> bool:
     """Check if the upgrade header is supported."""
-    return headers.get(hdrs.UPGRADE, "").lower() in {"tcp", "websocket"}
+    u = headers.get(hdrs.UPGRADE, "")
+    # .lower() can transform non-ascii characters.
+    return u.isascii() and u.lower() in {"tcp", "websocket"}
 
 
 class HttpParser(abc.ABC, Generic[_MsgT]):
@@ -664,7 +666,9 @@ class HttpRequestParser(HttpParser[RawRequestMessage]):
         )
 
     def _is_chunked_te(self, te: str) -> bool:
-        if te.rsplit(",", maxsplit=1)[-1].strip(" \t").lower() == "chunked":
+        te = te.rsplit(",", maxsplit=1)[-1].strip(" \t")
+        # .lower() transforms some non-ascii chars, so must check first.
+        if te.isascii() and te.lower() == "chunked":
             return True
         # https://www.rfc-editor.org/rfc/rfc9112#section-6.3-2.4.3
         raise BadHttpMessage("Request has invalid `Transfer-Encoding`")
diff --git a/tests/test_http_parser.py b/tests/test_http_parser.py
index 385452c..d4c1768 100644
--- a/tests/test_http_parser.py
+++ b/tests/test_http_parser.py
@@ -468,7 +468,21 @@ def test_request_chunked(parser) -> None:
     assert isinstance(payload, streams.StreamReader)
 
 
-def test_request_te_chunked_with_content_length(parser: Any) -> None:
+def test_te_header_non_ascii(parser: HttpRequestParser) -> None:
+    # K = Kelvin sign, not valid ascii.
+    text = "GET /test HTTP/1.1\r\nTransfer-Encoding: chunKed\r\n\r\n"
+    with pytest.raises(http_exceptions.BadHttpMessage):
+        parser.feed_data(text.encode())
+
+
+def test_upgrade_header_non_ascii(parser: HttpRequestParser) -> None:
+    # K = Kelvin sign, not valid ascii.
+    text = "GET /test HTTP/1.1\r\nUpgrade: websocKet\r\n\r\n"
+    messages, upgrade, tail = parser.feed_data(text.encode())
+    assert not upgrade
+
+
+def test_request_te_chunked_with_content_length(parser: HttpRequestParser) -> None:
     text = (
         b"GET /test HTTP/1.1\r\n"
         b"content-length: 1234\r\n"