Linux Distros Unpatched Vulnerability : CVE-2026-39821

high Nessus Plugin ID 317039

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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.

- The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII- only label. For example, ToUnicode(xn--example-.com) incorrectly returns the name example.com rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject example.com but permit xn--example-.com. If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name example.com. (CVE-2026-39821)

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

Solution

There is no known solution at this time.

Plugin Details

Severity: High

ID: 317039

File Name: unpatched_CVE_2026_39821.nasl

Version: 1.36

Type: Local

Agent: unix

Family: Misc.

Published: 5/27/2026

Updated: 11/14/2026

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

Risk Information

VPR

Risk Factor: Medium

Score: 4.8

Percentile: 58.1

CVSS v2

Risk Factor: High

Base Score: 9

Temporal Score: 7.7

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

CVSS Score Source: CVE-2026-39821

CVSS v3

Risk Factor: High

Base Score: 8.2

Temporal Score: 7.5

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

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

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:14.04:-:lts, 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:canonical:ubuntu_linux:26.10, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:13.0, p-cpe:/a:canonical:ubuntu_linux:adsys, p-cpe:/a:canonical:ubuntu_linux:containerd, p-cpe:/a:canonical:ubuntu_linux:golang-1.10, p-cpe:/a:canonical:ubuntu_linux:golang-1.13, p-cpe:/a:canonical:ubuntu_linux:golang-1.14, p-cpe:/a:canonical:ubuntu_linux:golang-1.16, p-cpe:/a:canonical:ubuntu_linux:golang-1.17, p-cpe:/a:canonical:ubuntu_linux:golang-1.18, p-cpe:/a:canonical:ubuntu_linux:golang-1.20, p-cpe:/a:canonical:ubuntu_linux:golang-1.21, p-cpe:/a:canonical:ubuntu_linux:golang-1.22, p-cpe:/a:canonical:ubuntu_linux:golang-1.23, p-cpe:/a:canonical:ubuntu_linux:golang-1.24, p-cpe:/a:canonical:ubuntu_linux:golang-1.25, p-cpe:/a:canonical:ubuntu_linux:golang-1.26, p-cpe:/a:canonical:ubuntu_linux:golang-1.27, p-cpe:/a:canonical:ubuntu_linux:golang-1.6, p-cpe:/a:canonical:ubuntu_linux:golang-1.8, p-cpe:/a:canonical:ubuntu_linux:golang-1.9, p-cpe:/a:canonical:ubuntu_linux:golang-golang-x-net, p-cpe:/a:canonical:ubuntu_linux:google-guest-agent, p-cpe:/a:canonical:ubuntu_linux:google-osconfig-agent, p-cpe:/a:canonical:ubuntu_linux:juju-core, p-cpe:/a:canonical:ubuntu_linux:lxd, p-cpe:/a:debian:debian_linux:golang-golang-x-net

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

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 5/22/2026

Reference Information

CVE: CVE-2026-39821

Detections

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