vulnerability / NVI-00014113 / Revision 1
Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie`
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01 / Meaning
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02 / Applicability
The affected context
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tornado
source listed>= 6.5.5, < 6.5.8
## 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. ```python 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.CookieError ``` The 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 trailing `if kwargs:` loop does `morsel[k] = v` with no ch
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04 / Limits
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05 / Provenance
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- GHSA-wwv5-g3v4-889x ↗
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- Revision 1 ·
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