---
id: CVE-2026-50256
title: >-
  A stack-based buffer overflow flaw was found in the X.Org X server and
  Xwayland
summary: >-
  A stack-based buffer overflow flaw was found in the X.Org X server and
  Xwayland. A mismatch between the X server and the libXfont2 library's maximum
  font name length can cause a stack buffer overflow during font alias
  resolution. The ser…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-121
  - CWE-121
vendor: x.org
product: x_server
affected:
  - x_server < 21.1.23
  - xwayland < 24.1.12
  - enterprise_linux = 7.0
  - enterprise_linux = 8.0
  - enterprise_linux = 9.0
  - enterprise_linux = 10.0
patched:
  - x_server 21.1.23
  - xwayland 24.1.12
published: '2026-06-05'
updated: '2026-07-07'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-50256'
references:
  - url: 'https://access.redhat.com/errata/RHSA-2026:26562'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:26566'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:26590'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:26610'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:26709'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:28923'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:29844'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:36086'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/security/cve/CVE-2026-50256'
    label: secalert@redhat.com
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2485380'
    label: secalert@redhat.com
  - url: >-
      https://gitlab.freedesktop.org/xorg/xserver/-/commit/bb5158f962dc935e58ef8b4b5fcb31be201a6e07
    label: secalert@redhat.com
  - url: 'https://lists.x.org/archives/xorg-announce/2026-June/003702.html'
    label: secalert@redhat.com
  - url: 'https://redhat.atlassian.net/browse/PSIRTSUPT-16950'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:26562'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:26566'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:26590'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:26610'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:26709'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:28923'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:29844'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-50256'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2485380'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-50256.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
tags:
  - nvd
epss: 0.00157
epssPercentile: 0.05293
ingestedAt: '2026-07-07T08:52:24.877Z'
---

## Overview

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

## Affected

- `x_server < 21.1.23`
- `xwayland < 24.1.12`
- `enterprise_linux = 7.0`
- `enterprise_linux = 8.0`
- `enterprise_linux = 9.0`
- `enterprise_linux = 10.0`

## Remediation

Upgrade past the affected range:

- `x_server 21.1.23`
- `xwayland 24.1.12`