# CVE-2026-35536: Tornado cookie attribute injection in RequestHandler.set_cookie

Source: https://junglewise.ai/threats/cve-2026-35536-tornado-cookie-attribute-injection-in-requesthandler-set-cookie  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-03. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-35536 · Severity: high · CVSS 7.2 · Published 2026-04-03

Tornado is a popular web framework and networking library for Python. A security flaw in how it handles web cookies allows attackers to inject unauthorized cookie attributes, which could lead to session manipulation or security policy bypasses. This could potentially allow an attacker to compromise user accounts or interfere with how a browser interacts with the website.

Technologies: [tornado (PyPI)](https://junglewise.ai/threats/technologies/tornado). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-35536 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-35536 being exploited in the wild.

**How severe is CVE-2026-35536?** High severity, with a CVSS score of 7.2, published 3 April 2026.

**Which products and versions are affected?** tornado (PyPI) ECOSYSTEM:introduced=0,fixed=6.5.5.

**Is there a fix for CVE-2026-35536?** Yes. tornado (PyPI): upgrade to 6.5.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-35536 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-35536?** Check whether you run tornado (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- tornado (PyPI): upgrade to 6.5.5 or later

  ```sh
  pip install "tornado>=6.5.5"
  ```


## Technical details

A cookie attribute injection vulnerability exists in Tornado's RequestHandler.set_cookie method. The root cause is improper neutralization of special characters (specifically semicolons) within the 'domain', 'path', and 'samesite' arguments. An attacker who can influence these parameters can inject additional cookie attributes, potentially overriding security settings like 'HttpOnly' or 'Secure', or manipulating session behavior. This is reachable over the network without authentication, though it typically requires the application to pass user-controlled input into the affected cookie parameters. The issue is resolved in version 6.5.5.

## Affected products

- tornadoweb Tornado < 6.5.5

## Identifiers

- CVE-2026-35536
- GHSA-78cv-mqj4-43f7
- GHSA-fqwm-6jpj-5wxc
- PYSEC-2026-2287

## Timeline

- 2026-03-10: patched: Fixed in version 6.5.5
- 2026-03-10: advisory: GitHub Security Advisory published
- 2026-04-03: disclosed: CVE published to NVD

## References

- [https://github.com/tornadoweb/tornado/releases/tag/v6.5.5](https://github.com/tornadoweb/tornado/releases/tag/v6.5.5)
- [https://github.com/tornadoweb/tornado/security/advisories/GHSA-78cv-mqj4-43f7](https://github.com/tornadoweb/tornado/security/advisories/GHSA-78cv-mqj4-43f7)

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