Tornado has incomplete validation of cookie attributes

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.4 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-35536: 0.25% estimated exploitation activity in the next 30 days; percentile 15.96 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Values passed to the domain, path, and samesite arguments of RequestHandler.setcookie were not completely validated in versions of Tornado prior to 6.5.5. In particular, semicolons would be allowed, which could be used to inject attacker-controlled values for other cookie attributes.

Published by the source

11 Mar 2026, 22:17 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:37 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-78cv-mqj4-43f7

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-fqwm-6jpj-5wxc

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-78cv-mqj4-43f7

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# Patch Next advisory brief: CVE-2026-35536

Advisory: Tornado has incomplete validation of cookie attributes
IDs: CVE-2026-35536, GHSA-78cv-mqj4-43f7
Record: https://patchnext.com/advisories/cve-2026-35536 (revision 3, source checked 26 Oct 2026, 13:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tornado 6.5.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI tornado: affected <= 6.5.4; fixed in 6.5.5

## Suggested inspection (read-only)
- `python -m pip show tornado`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on tornado.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-78cv-mqj4-43f7 (OSV record GHSA-78cv-mqj4-43f7 lists affected ranges: PyPI tornado >=0 <6.5.5 (fixed))
- Verified: https://osv.dev/vulnerability/GHSA-fqwm-6jpj-5wxc (OSV record GHSA-fqwm-6jpj-5wxc lists affected ranges: PyPI tornado >=0 <6.5.5 (fixed))
- Verified: https://github.com/advisories/GHSA-78cv-mqj4-43f7 (GitHub-reviewed advisory GHSA-78cv-mqj4-43f7 lists affected ranges: PyPI tornado >=0 <=6.5.4)

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