Linux Distros Unpatched Vulnerability : CVE-2026-56855

high Nessus Plugin ID 342721

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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.

- Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all other messages as a protocol error and tear the connection down instead of buffering and blocking. (CVE-2026-56855)

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: 342721

File Name: unpatched_CVE_2026_56855.nasl

Version: 1.4

Type: Local

Agent: unix

Family: Misc.

Published: 9/4/2026

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: 3

Percentile: 23.61

CVSS v2

Risk Factor: Medium

Base Score: 4.3

Temporal Score: 3.7

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

CVSS Score Source: CVE-2026-56855

CVSS v3

Risk Factor: High

Base Score: 7.5

Temporal Score: 6.9

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

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

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:centos:centos:8, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:13.0, cpe:/o:redhat:enterprise_linux:10, cpe:/o:redhat:enterprise_linux:8, cpe:/o:redhat:enterprise_linux:9, p-cpe:/a:canonical:ubuntu_linux:golang-1.17, 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-defaults, p-cpe:/a:centos:centos:buildah-tests, p-cpe:/a:centos:centos:buildah, p-cpe:/a:centos:centos:grafana-selinux, p-cpe:/a:centos:centos:grafana, p-cpe:/a:centos:centos:gvisor-tap-vsock-gvforwarder, p-cpe:/a:centos:centos:gvisor-tap-vsock, p-cpe:/a:centos:centos:podman-catatonit, p-cpe:/a:centos:centos:podman-docker, p-cpe:/a:centos:centos:podman-gvproxy, p-cpe:/a:centos:centos:podman-manpages, p-cpe:/a:centos:centos:podman-plugins, p-cpe:/a:centos:centos:podman-remote, p-cpe:/a:centos:centos:podman-tests, p-cpe:/a:centos:centos:podman, p-cpe:/a:debian:debian_linux:golang-go.crypto, p-cpe:/a:redhat:enterprise_linux:buildah-tests, p-cpe:/a:redhat:enterprise_linux:buildah, p-cpe:/a:redhat:enterprise_linux:grafana-selinux, p-cpe:/a:redhat:enterprise_linux:grafana, p-cpe:/a:redhat:enterprise_linux:gvisor-tap-vsock-gvforwarder, p-cpe:/a:redhat:enterprise_linux:gvisor-tap-vsock, p-cpe:/a:redhat:enterprise_linux:podman-catatonit, p-cpe:/a:redhat:enterprise_linux:podman-docker, p-cpe:/a:redhat:enterprise_linux:podman-gvproxy, p-cpe:/a:redhat:enterprise_linux:podman-manpages, p-cpe:/a:redhat:enterprise_linux:podman-plugins, p-cpe:/a:redhat:enterprise_linux:podman-remote, p-cpe:/a:redhat:enterprise_linux:podman-tests, p-cpe:/a:redhat:enterprise_linux:podman

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: 9/2/2026

Reference Information

CVE: CVE-2026-56855

Detections

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