BREW-SICKCHILL-GHSA-WWV5… (GHSA-WWV5-G3V4-889X)
Vulnerability from osv_homebrew – Published: 2026-09-02 09:54 – Updated: 2026-09-17 18:24 – Source websiteSummary
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.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 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).
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "tornado",
"resource_purl": "pkg:pypi/tornado@6.5.8",
"upstream_fixed_in": "6.5.8"
},
"package": {
"ecosystem": "Homebrew",
"name": "sickchill",
"purl": "pkg:brew/sickchill"
},
"ranges": [
{
"events": [
{
"introduced": "2024.3.1_5"
},
{
"fixed": "2024.3.1_8"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/tornado@6.5.8",
"name": "tornado",
"resource": "tornado",
"strategy": "registry",
"subject_version": "6.5.8"
}
]
},
"details": "## Summary\nThe CVE-2026-35536 fix added a validation loop that rejects `[\\x00-\\x20\\x3b\\x7f]`, but only for the\nhardcoded **lowercase** keys `name`/`domain`/`path`/`samesite`. The still-live deprecated `**kwargs` path\nwrites attacker-supplied attribute values straight into the `Morsel` with no validation, and because\n`Morsel.__setitem__` is case-insensitive, a capitalized kwarg (`Domain=`, `Path=`, `SameSite=`, `Max-Age=`)\nroutes to the same reserved attribute while bypassing the loop \u2014 re-opening `;`-delimited attribute injection.\n\n```python\nself.set_cookie(\"sid\", \"abc\", Domain=\"evil.com; Secure; SameSite=None\")\n# -\u003e Set-Cookie: sid=abc; Domain=evil.com; Secure; SameSite=None; Path=/\n# Sanity (the canonical lowercase named arg IS blocked):\nself.set_cookie(\"sid\", \"abc\", domain=\"evil.com; Secure\") # -\u003e http.cookies.CookieError\n```\n\nThe patch\u0027s regression test (`SetCookieForbiddenCharHandler`) only exercises the four named params, never the\n`**kwargs` path, so the gap is not regression-covered.\n\n## Affected code\n- `tornado/web.py` \u2192 `RequestHandler.set_cookie`: the validation loop covers only the lowercase named args;\n the trailing `if kwargs:` loop does `morsel[k] = v` with no character validation.\n\n## Steps to reproduce\n`GET /upper` (uses `Domain=` kwarg) emits `Set-Cookie: c_upper=v; Domain=evil.com; Secure; SameSite=None; Path=/`; `GET /lower` (uses lowercase\n`domain=`) returns a `CookieError`.\n\n## Impact\nInjection of independent cookie attributes (force/drop `Secure`/`HttpOnly`/`SameSite`, rebind `Domain`/`Path`)\n\u2014 the same impact CVE-2026-35536 closed, via the sibling path the patch missed. Conditional on the app using\na capitalized/legacy keyword.\n\n## Suggested remediation\nApply the same `[\\x00-\\x20\\x3b\\x7f]` validation to every entry in the `**kwargs` loop (after normalizing the\nkey case), or remove the deprecated kwargs path; add a regression test for capitalized kwargs.\n\n## Credit\nReported as part of an incomplete-patch measurement study (responsible disclosure).",
"id": "BREW-sickchill-GHSA-wwv5-g3v4-889x",
"modified": "2026-09-17T18:24:58Z",
"published": "2026-09-02T09:54:19Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x"
},
{
"type": "WEB",
"url": "https://github.com/tornadoweb/tornado/pull/3704"
},
{
"type": "WEB",
"url": "https://github.com/tornadoweb/tornado/pull/3706"
},
{
"type": "WEB",
"url": "https://github.com/tornadoweb/tornado/commit/6ef836e43e1278530041376adb32504daa977b91"
},
{
"type": "WEB",
"url": "https://github.com/tornadoweb/tornado/commit/da284767eae8e1f0484f123b8c3225f6465b09c7"
},
{
"type": "PACKAGE",
"url": "https://github.com/tornadoweb/tornado"
},
{
"type": "WEB",
"url": "https://github.com/tornadoweb/tornado/releases/tag/v6.5.8"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "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",
"type": "CVSS_V4"
}
],
"summary": "Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie`",
"upstream": [
"GHSA-wwv5-g3v4-889x",
"CVE-2026-91991"
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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