Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie`
Summary
The CVE-2026-35536 fix added a validation loop that rejects [\x00-\x20\x3b\x7f], but only for the
hardcoded lowercase keys name/domain/path/samesite. The still-live deprecated **kwargs path
writes attacker-supplied attribute values straight into the Morsel with no validation, and because
Morsel.__setitem__ is case-insensitive, a capitalized kwarg (Domain=, Path=, SameSite=, Max-Age=)
routes to the same reserved attribute while bypassing the loop — re-opening ;-delimited attribute injection.
self.set_cookie("sid", "abc", Domain="evil.com; Secure; SameSite=None")
# -> Set-Cookie: sid=abc; Domain=evil.com; Secure; SameSite=None; Path=/
# Sanity (the canonical lowercase named arg IS blocked):
self.set_cookie("sid", "abc", domain="evil.com; Secure") # -> http.cookies.CookieErrorThe patch's regression test (SetCookieForbiddenCharHandler) only exercises the four named params, never the
**kwargs path, so the gap is not regression-covered.
Affected code
tornado/web.py→RequestHandler.set_cookie: the validation loop covers only the lowercase named args; the trailingif kwargs:loop doesmorsel[k] = vwith no character validation.
Steps to reproduce
GET /upper (uses Domain= kwarg) emits Set-Cookie: c_upper=v; Domain=evil.com; Secure; SameSite=None; Path=/; GET /lower (uses lowercase
domain=) returns a CookieError.
Impact
Injection of independent cookie attributes (force/drop Secure/HttpOnly/SameSite, rebind Domain/Path)
— the same impact CVE-2026-35536 closed, via the sibling path the patch missed. Conditional on the app using
a capitalized/legacy keyword.
Suggested remediation
Apply the same [\x00-\x20\x3b\x7f] validation to every entry in the **kwargs loop (after normalizing the
key case), or remove the deprecated kwargs path; add a regression test for capitalized kwargs.
Credit
Reported as part of an incomplete-patch measurement study (responsible disclosure).
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Python (PyPI) | tornado | >= 6.5.5, < 6.5.8 | 6.5.8 |
Referencias
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x
- https://github.com/tornadoweb/tornado/pull/3704
- https://github.com/tornadoweb/tornado/pull/3706
- https://github.com/tornadoweb/tornado/commit/6ef836e43e1278530041376adb32504daa977b91
- https://github.com/tornadoweb/tornado/commit/da284767eae8e1f0484f123b8c3225f6465b09c7
- https://github.com/tornadoweb/tornado
- https://github.com/tornadoweb/tornado/releases/tag/v6.5.8
- Vector CVSS
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N- Debilidad (CWE)
CWE-74- Plataforma
- Python (PyPI)
- Paquete
tornado- Publicada
- 01.09.2026
- Actualizado
- 11.10.2026 15:18
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-wwv5-g3v4-889x - CC BY 4.0
Historial de vulnerabilidades: tornado
Todas las vulnerabilidades publicadas de este paquete (Python (PyPI)), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 23
- Primera → última
- 05.2012 09.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Alta 13
- Media 8
- Baja 2
Divulgaciones por año
- 2017: 0
- 2018: 0
- 2019: 0
- 2020: 1
- 2021: 0
- 2022: 0
- 2023: 2
- 2024: 3
- 2025: 4
- 2026: 12
antes: 1
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Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie` esta entrada
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