Fix cookie header parser ignoring reserved names (#11178)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: bdraco

CHANGES/11178.bugfix.rst

@@ -0,0 +1 @@
+Fixed ``Cookie`` header parsing to treat attribute names as regular cookies per :rfc:`6265#section-5.4` -- by :user:`bdraco`.

aiohttp/_cookie_helpers.py

@@ -12,7 +12,11 @@
 
 from .log import internal_logger
 
-__all__ = ("parse_cookie_headers", "preserve_morsel_with_coded_value")
+__all__ = (
+    "parse_set_cookie_headers",
+    "parse_cookie_header",
+    "preserve_morsel_with_coded_value",
+)
 
 # Cookie parsing constants
 # Allow more characters in cookie names to handle real-world cookies
@@ -153,7 +157,62 @@ def _unquote(value: str) -> str:
     return _unquote_sub(_unquote_replace, value)
 
 
-def parse_cookie_headers(headers: Sequence[str]) -> List[Tuple[str, Morsel[str]]]:
+def parse_cookie_header(header: str) -> List[Tuple[str, Morsel[str]]]:
+    """
+    Parse a Cookie header according to RFC 6265 Section 5.4.
+
+    Cookie headers contain only name-value pairs separated by semicolons.
+    There are no attributes in Cookie headers - even names that match
+    attribute names (like 'path' or 'secure') should be treated as cookies.
+
+    This parser uses the same regex-based approach as parse_set_cookie_headers
+    to properly handle quoted values that may contain semicolons.
+
+    Args:
+        header: The Cookie header value to parse
+
+    Returns:
+        List of (name, Morsel) tuples for compatibility with SimpleCookie.update()
+    """
+    if not header:
+        return []
+
+    cookies: List[Tuple[str, Morsel[str]]] = []
+    i = 0
+    n = len(header)
+
+    while i < n:
+        # Use the same pattern as parse_set_cookie_headers to find cookies
+        match = _COOKIE_PATTERN.match(header, i)
+        if not match:
+            break
+
+        key = match.group("key")
+        value = match.group("val") or ""
+        i = match.end(0)
+
+        # Validate the name
+        if not key or not _COOKIE_NAME_RE.match(key):
+            internal_logger.warning("Can not load cookie: Illegal cookie name %r", key)
+            continue
+
+        # Create new morsel
+        morsel: Morsel[str] = Morsel()
+        # Preserve the original value as coded_value (with quotes if present)
+        # We use __setstate__ instead of the public set() API because it allows us to
+        # bypass validation and set already validated state. This is more stable than
+        # setting protected attributes directly and unlikely to change since it would
+        # break pickling.
+        morsel.__setstate__(  # type: ignore[attr-defined]
+            {"key": key, "value": _unquote(value), "coded_value": value}
+        )
+
+        cookies.append((key, morsel))
+
+    return cookies
+
+
+def parse_set_cookie_headers(headers: Sequence[str]) -> List[Tuple[str, Morsel[str]]]:
     """
     Parse cookie headers using a vendored version of SimpleCookie parsing.
 

aiohttp/abc.py

@@ -22,7 +22,7 @@
 from multidict import CIMultiDict
 from yarl import URL
 
-from ._cookie_helpers import parse_cookie_headers
+from ._cookie_helpers import parse_set_cookie_headers
 from .typedefs import LooseCookies
 
 if TYPE_CHECKING:
@@ -194,7 +194,7 @@ def update_cookies_from_headers(
         self, headers: Sequence[str], response_url: URL
     ) -> None:
         """Update cookies from raw Set-Cookie headers."""
-        if headers and (cookies_to_update := parse_cookie_headers(headers)):
+        if headers and (cookies_to_update := parse_set_cookie_headers(headers)):
             self.update_cookies(cookies_to_update, response_url)
 
     @abstractmethod

aiohttp/client_reqrep.py

@@ -30,7 +30,11 @@
 from yarl import URL
 
 from . import hdrs, helpers, http, multipart, payload
-from ._cookie_helpers import parse_cookie_headers, preserve_morsel_with_coded_value
+from ._cookie_helpers import (
+    parse_cookie_header,
+    parse_set_cookie_headers,
+    preserve_morsel_with_coded_value,
+)
 from .abc import AbstractStreamWriter
 from .client_exceptions import (
     ClientConnectionError,
@@ -313,9 +317,9 @@ def cookies(self) -> SimpleCookie:
             if self._raw_cookie_headers is not None:
                 # Parse cookies for response.cookies (SimpleCookie for backward compatibility)
                 cookies = SimpleCookie()
-                # Use parse_cookie_headers for more lenient parsing that handles
+                # Use parse_set_cookie_headers for more lenient parsing that handles
                 # malformed cookies better than SimpleCookie.load
-                cookies.update(parse_cookie_headers(self._raw_cookie_headers))
+                cookies.update(parse_set_cookie_headers(self._raw_cookie_headers))
                 self._cookies = cookies
             else:
                 self._cookies = SimpleCookie()
@@ -1014,8 +1018,8 @@ def update_cookies(self, cookies: Optional[LooseCookies]) -> None:
 
         c = SimpleCookie()
         if hdrs.COOKIE in self.headers:
-            # parse_cookie_headers already preserves coded values
-            c.update(parse_cookie_headers((self.headers.get(hdrs.COOKIE, ""),)))
+            # parse_cookie_header for RFC 6265 compliant Cookie header parsing
+            c.update(parse_cookie_header(self.headers.get(hdrs.COOKIE, "")))
             del self.headers[hdrs.COOKIE]
 
         if isinstance(cookies, Mapping):

aiohttp/web_request.py

@@ -28,7 +28,7 @@
 from yarl import URL
 
 from . import hdrs
-from ._cookie_helpers import parse_cookie_headers
+from ._cookie_helpers import parse_cookie_header
 from .abc import AbstractStreamWriter
 from .helpers import (
     _SENTINEL,
@@ -556,9 +556,10 @@ def cookies(self) -> Mapping[str, str]:
 
         A read-only dictionary-like object.
         """
-        # Use parse_cookie_headers for more lenient parsing that accepts
-        # special characters in cookie names (fixes #2683)
-        parsed = parse_cookie_headers((self.headers.get(hdrs.COOKIE, ""),))
+        # Use parse_cookie_header for RFC 6265 compliant Cookie header parsing
+        # that accepts special characters in cookie names (fixes #2683)
+        parsed = parse_cookie_header(self.headers.get(hdrs.COOKIE, ""))
+        # Extract values from Morsel objects
         return MappingProxyType({name: morsel.value for name, morsel in parsed})
 
     @reify