CVE-2026-35536: Tornado Tornado Has Cookie Attribute Injection Vulnerability

HIGH
Advisory Identifier: GHSA-fqwm-6jpj-5wxc
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CVSS 7.2
CWE-159
Published
Advisory Summary

CVE-2026-35536 is a HIGH (CVSS 7.2) tornado has cookie attribute injection vulnerability (CWE-159: Improper Handling of Invalid Use of Special Elements) affecting Tornado libraries in the PyPI ecosystem. The issue involves tornado has cookie attribute injection via .requesthandler.set_cookie. Remediation is available by upgrading affected packages to version 6.5.5.

CVE-2026-35536 at a Glance

CVE Identifier CVE-2026-35536
GHSA Identifier GHSA-fqwm-6jpj-5wxc
Severity HIGH
CVSS v3.1 Base Score 7.2
CWE Classification CWE-159: Improper Handling of Invalid Use of Special Elements
Affected Product Tornado
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.2

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-35536

To remediate this vulnerability, upgrade all affected Tornado dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

tornado fixed: 6.5.5 
pip install tornado>=6.5.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show tornado

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-35536, inspect your installed packages using pip:

pip show tornado

Analyze the terminal output to locate any version of Tornado in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.5.5), your application is affected.

Note: The pip show tornado command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-159: Improper Handling of Invalid Use of Special Elements, where the product does not properly filter, remove, quote, or otherwise manage the invalid use of special elements in user-controlled input, which could cause adverse effect on its behavior and integrity. In Tornado, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

In Tornado before 6.5.5, cookie attribute injection could occur because the domain, path, and samesite arguments to `.RequestHandler.set_cookie` were not checked for crafted characters.

CVE-2026-35536 Affected Tornado Versions

1 component(s)
Fixed Versions:
6.5.5
Product / Package Ecosystem Affected Versions Fixed Version
tornado
pypi/tornado
PyPI
< 6.5.5
6.5.5

References

GitHub Advisory / Wiki ADVISORY
https://github.com/tornadoweb/tornado/security/advisories/GHSA-78cv-mqj4-43f7
NVD — CVE-2026-35536 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35536
Tornado Source Repository REPOSITORY
https://github.com/tornadoweb/tornado
Tornado Release RELEASE
https://github.com/tornadoweb/tornado/releases/tag/v6.5.5

Frequently Asked Questions

What is CVE-2026-35536?
CVE-2026-35536 is a security vulnerability in Tornado involving Tornado has cookie attribute injection via .RequestHandler.set_cookie under CWE-159: Improper Handling of Invalid Use of Special Elements.
Which Tornado versions are affected?
Affected versions include releases prior to 6.5.5 across affected packages: tornado.
What version fixes CVE-2026-35536?
Upgrading to 6.5.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is tornado affected?
Yes, tornado is affected in releases prior to 6.5.5. Upgrade your dependency to 6.5.5 or later.
What is the CVSS score of CVE-2026-35536?
CVE-2026-35536 has a CVSS v3.1 base score of 7.2 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2026-35536?
CVE-2026-35536 is classified under CWE-159: Improper Handling of Invalid Use of Special Elements (The product does not properly filter, remove, quote, or otherwise manage the invalid use of special elements in user-controlled input, which could cause adverse effect on its behavior and integrity.).
How can I check PyPI dependencies for CVE-2026-35536?
Run the dependency tree command: 'pip show tornado'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-fqwm-6jpj-5wxc",
  "modified" : "2026-04-04T06:45:00Z",
  "published" : "2026-04-03T06:31:31Z",
  "aliases" : [ "CVE-2026-35536" ],
  "summary" : "Tornado has cookie attribute injection via .RequestHandler.set_cookie",
  "details" : "In Tornado before 6.5.5, cookie attribute injection could occur because the domain, path, and samesite arguments to `.RequestHandler.set_cookie` were not checked for crafted characters.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "tornado"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.5.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/tornadoweb/tornado/security/advisories/GHSA-78cv-mqj4-43f7"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35536"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/tornadoweb/tornado"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tornadoweb/tornado/releases/tag/v6.5.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-159" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-04T06:45:00Z",
    "nvd_published_at" : "2026-04-03T04:16:53Z"
  }
}