CVE-2026-91991Public exploitNetwork attack vectorHinoki check available

Cookie attribute injection via unvalidated mixed-case kwargs

Published Sep 15, 2026 · Updated Sep 15, 2026

Cookie attribute injection in tornadoweb Tornado 6.5.5 through 6.5.7 allows remote attackers to alter browser cookie protections. RequestHandler.set_cookie validates only lowercase named attributes, while its deprecated keyword-argument loop writes mixed-case values directly into a case-insensitive Morsel. Exploitation requires an application to route untrusted data through a capitalized legacy attribute; semicolons can add Secure, HttpOnly, SameSite, Domain, or Path directives.

CVSS severity2.3
Low
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Cookie attribute injection in tornadoweb Tornado 6.5.5 through 6.5.7 allows remote attackers to alter browser cookie protections. RequestHandler.set_cookie validates only lowercase named attributes, while its deprecated keyword-argument loop writes mixed-case values directly into a case-insensitive Morsel. Exploitation requires an application to route untrusted data through a capitalized legacy attribute; semicolons can add Secure, HttpOnly, SameSite, Domain, or Path directives.

The record

CVE
CVE-2026-91991
Published
Sep 15, 2026
Updated
Sep 15, 2026
Vendor
tornadoweb
Product
Tornado
Classifications
CWE-74
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 15, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.5.5 <6.5.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

tornadoweb · Tornadoversion=6.5.5 <6.5.8

Published CVSS scores

2.3GitHub Security Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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