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Linux Distros Unpatched Vulnerability : CVE-2026-91991

medium Nessus Plugin ID 345996

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Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

 - Tornado before 6.5.8 contains an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by passing capitalized or legacy keyword arguments to set_cookie.
 Attackers can embed semicolon-delimited data in capitalized parameters like Domain, Path, or SameSite to bypass validation and modify cookie security attributes. (CVE-2026-91991)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

See Also

https://security-tracker.debian.org/tracker/CVE-2026-91991

https://ubuntu.com/security/CVE-2026-91991

Plugin Details

Severity: Medium

ID: 345996

File Name: unpatched_CVE_2026_91991.nasl

Version: 1.5

Type: Local

Agent: unix

Family: Misc.

Published: 9/15/2026

Updated: 9/24/2026

Supported Sensors: Agentless Assessment, Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 2.3

Percentile: 10.04

CVSS v2

Risk Factor: Medium

Base Score: 4

Temporal Score: 3.4

Vector: CVSS2#AV:N/AC:H/Au:N/C:P/I:P/A:N

CVSS Score Source: CVE-2026-91991

CVSS v3

Risk Factor: Medium

Base Score: 5.4

Temporal Score: 5

Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

Temporal Vector: CVSS:3.0/E:U/RL:U/RC:C

CVSS v4

Risk Factor: Medium

Base Score: 6.3

Threat Score: 1.7

Threat Vector: CVSS:4.0/E:U

Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, cpe:/o:canonical:ubuntu_linux:24.04:-:lts, cpe:/o:canonical:ubuntu_linux:26.04:-:lts, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:14.0, p-cpe:/a:canonical:ubuntu_linux:python-tornado, p-cpe:/a:debian:debian_linux:python-tornado

Required KB Items: Host/cpu, Host/local_checks_enabled, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 9/15/2026

Reference Information

CVE: CVE-2026-91991