Linux Distros Unpatched Vulnerability : CVE-2026-50258

high Nessus Plugin ID 318748

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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.

- A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. The X server has multiple stack buffers sized XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify or clamp non- canonical key types to XkbMaxShiftLevel. A client can change key types to excessive shift levels and trigger stack overflows. This is caused by an incomplete fix of CVE-2025-26597. This may be used to crash the server, or for privilege escalation if the X server runs as root. (CVE-2026-50258)

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: 318748

File Name: unpatched_CVE_2026_50258.nasl

Version: 1.15

Type: Local

Agent: unix

Family: Misc.

Published: 6/5/2026

Updated: 7/7/2026

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: Medium

Score: 4.9

Percentile: 57.98

CVSS v2

Risk Factor: High

Base Score: 7.2

Temporal Score: 6.1

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

CVSS Score Source: CVE-2026-50258

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 7.1

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

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

Vulnerability Information

CPE: cpe:/o:debian:debian_linux:11.0, cpe:/o:centos:centos:7, cpe:/o:redhat:enterprise_linux:6, cpe:/o:redhat:enterprise_linux:7, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, p-cpe:/a:centos:centos:tigervnc, p-cpe:/a:centos:centos:tigervnc-icons, p-cpe:/a:centos:centos:tigervnc-license, p-cpe:/a:centos:centos:tigervnc-server, p-cpe:/a:centos:centos:tigervnc-server-applet, p-cpe:/a:centos:centos:tigervnc-server-minimal, p-cpe:/a:centos:centos:tigervnc-server-module, p-cpe:/a:debian:debian_linux:xwayland, p-cpe:/a:debian:debian_linux:xorg-server, p-cpe:/a:redhat:enterprise_linux:tigervnc, p-cpe:/a:redhat:enterprise_linux:tigervnc-icons, p-cpe:/a:redhat:enterprise_linux:tigervnc-license, p-cpe:/a:redhat:enterprise_linux:tigervnc-server, p-cpe:/a:redhat:enterprise_linux:tigervnc-server-applet, p-cpe:/a:redhat:enterprise_linux:tigervnc-server-minimal, p-cpe:/a:redhat:enterprise_linux:tigervnc-server-module, p-cpe:/a:canonical:ubuntu_linux:xwayland, cpe:/o:canonical:ubuntu_linux:14.04:-:lts, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, cpe:/o:debian:debian_linux:12.0, cpe:/o:canonical:ubuntu_linux:24.04:-:lts, cpe:/o:debian:debian_linux:13.0, p-cpe:/a:canonical:ubuntu_linux:xorg-server-hwe-16.04, p-cpe:/a:canonical:ubuntu_linux:xorg-server-hwe-18.04, p-cpe:/a:canonical:ubuntu_linux:xorg-server, cpe:/o:canonical:ubuntu_linux:25.10, cpe:/o:canonical:ubuntu_linux:26.04:-:lts

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

Exploit Ease: No known exploits are available

Reference Information

CVE: CVE-2026-50258

Detections

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