CentOS Stream 10 — xorg-x11-server-Xwayland — multiple vulnerabilities (6 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: AlmaLinux/RHEL advisory ALSA-2026:11352

Related CVEs: CVE-2026-33999 CVE-2026-34001 CVE-2026-34003 CVE-2025-62229 CVE-2025-62230 CVE-2025-62231

Upstream summary: Xwayland is an X server for running X clients under Wayland.

Security Fix(es):

* xorg: xwayland: X.Org X server: Denial of Service via integer underflow in XKB compatibility map handling (CVE-2026-33999)
* xorg: xwayland: X.Org X server: Use-after-free vulnerability leads to server crash and potential memory corruption (CVE-2026-34001)
* xorg: xwayland: X.Org X server: Information exposure and denial of service via out-of-bounds memory access (CVE-2026-34003)

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Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Exploitation of xorg-x11-server-Xwayland is user-driven: the danger arrives when someone opens a hostile page, message or attachment, so exposure sits on each CentOS Stream 10 workstation rather than on any serving path. Desktop sessions run for weeks, and the package manager only replaces files on disk — a xorg-x11-server-Xwayland process started before the update keeps the old code mapped until the user quits and relaunches it. Consequences are local: theft of saved credentials and session cookies, access to the user’s profile data under $HOME, and code execution as the logged-in account. xorg-x11-server-Xwayland is a graphical application launched by a user from their desktop session, not a system service: there is no unit to restart, and systemctl or journalctl will report nothing for it.

Environment & Reproduction

Reproduction targets CentOS Stream 10. Confirm release and the installed package:

cat /etc/centos-release
cat /etc/os-release
rpm -q xorg-x11-server-Xwayland
dnf info xorg-x11-server-Xwayland | head -20

Exercise the workload that uses xorg-x11-server-Xwayland while collecting:

sudo journalctl -xe --no-pager | tail -200
sudo tail -200 /var/log/dnf.log
sudo tail -200 /var/log/audit/audit.log
# For an evidence bundle bundle with sosreport:
sudo sosreport --batch

Root Cause Analysis

Root cause is documented in AlmaLinux/RHEL advisory ALSA-2026:11352. AlmaLinux / Red Hat maintainers shipped fixes in the corresponding xorg-x11-server-Xwayland update for CentOS Stream 10; running an outdated build leaves the host exposed to the failure modes described in the advisory. Correlate dnf history with system logs:

sudo dnf history | head
sudo dnf history list xorg-x11-server-Xwayland
sudo dnf history info <id>
sudo ausearch -m AVC,USER_AVC -ts today | tail -100
cat /proc/sys/kernel/tainted   # non-zero = tainted kernel / out-of-tree modules

Quick Triage

Run these on CentOS Stream 10 to capture the current state of xorg-x11-server-Xwayland:

rpm -q xorg-x11-server-Xwayland                              # installed NVR
rpm -V xorg-x11-server-Xwayland                              # verify shipped files
sudo dnf check-update --security
sudo dnf updateinfo list cves
systemctl --failed --no-pager
sudo firewall-cmd --list-all
getenforce && sestatus
dnf repoquery -l xorg-x11-server-Xwayland 2>/dev/null | grep -E '/lib/systemd/system/.*\.(service|socket|timer)$'  # same check WITHOUT installing (EL7/Amazon Linux 2: yum install yum-utils, then: repoquery -l xorg-x11-server-Xwayland)
systemctl show --no-pager -p Type,RemainAfterExit <UNIT>  # Type=oneshot (often paired with a .timer) means a one-shot job, NOT a daemon -- do not 'restart' it, let the timer fire

Step-by-Step Diagnosis

1. List failed systemd units.

   systemctl --failed --no-pager

2. Tail the journal for xorg-x11-server-Xwayland and the system bus.

   sudo journalctl -xe -f --no-pager

3. Inspect firewall posture.

   sudo firewall-cmd --list-all-zones --permanent
   sudo nft list ruleset 2>/dev/null | head -50

4. Surface SELinux denials and author a local policy module if needed.

   sudo ausearch -m AVC,USER_AVC -ts today
   sudo ausearch -m AVC -ts today | audit2allow -a -M /tmp/local-fix
   sudo semodule -i /tmp/local-fix.pp

5. Verify xorg-x11-server-Xwayland integrity and reinstall if anything is altered.

   sudo rpm -V xorg-x11-server-Xwayland
   sudo dnf reinstall xorg-x11-server-Xwayland

6. Correlate findings with /var/log/dnf.log, dnf history, and AlmaLinux/RHEL advisory ALSA-2026:11352 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective dnf transaction referenced by AlmaLinux/RHEL advisory ALSA-2026:11352, then reload affected systemd units:

sudo dnf -y makecache
sudo dnf -y upgrade --security              # apply ALL security errata (recommended)
# Or target a single package:
sudo dnf -y upgrade xorg-x11-server-Xwayland
# Unit name may differ from pkg name; check first:
rpm -q xorg-x11-server-Xwayland                                # confirm new NVR

For kernel / glibc / systemd / openssl advisories a reboot is required (or kpatch where licensed):

sudo needs-restarting -r                    # report whether reboot needed
sudo systemctl reboot                       # or: sudo shutdown -r now
# kpatch (Red Hat / Oracle) avoids reboot for many kernel CVEs:
sudo dnf install -y kpatch kpatch-dnf
sudo dnf kpatch auto                        # enable auto-patching
sudo kpatch list

Solution – Alternative Approaches

If the primary patch is not viable, choose from these:

• Roll back the offending dnf transaction:

  sudo dnf history list | head
  sudo dnf history info <id>
  sudo dnf history undo <id>

• Version-lock the package so dnf cannot upgrade it:

  sudo dnf install -y python3-dnf-plugin-versionlock
  sudo dnf versionlock add xorg-x11-server-Xwayland
  sudo dnf versionlock list
  sudo dnf versionlock delete xorg-x11-server-Xwayland      # remove the lock

• Install an older NVR if a regression is suspected:

  dnf --showduplicates list xorg-x11-server-Xwayland | tac | head
  sudo dnf install -y --allowerasing xorg-x11-server-Xwayland-<older-NVR>

• Switch SELinux to permissive briefly to confirm policy is the cause, then re-enforce:

  sudo setenforce 0
  # reproduce, capture denials, author a custom module:
  sudo ausearch -m AVC -ts recent | audit2allow -a -M mylocal
  sudo semodule -i mylocal.pp
  sudo setenforce 1

• Take an LVM snapshot before kernel / glibc upgrades for fast rollback:

  sudo lvs
  sudo lvcreate -s -n preupgrade -L 4G /dev/<vg>/<lv>
  # revert later via:
  sudo lvconvert --merge /dev/<vg>/preupgrade && sudo systemctl reboot

• Where kpatch is licensed, apply kernel fixes without reboot:

  sudo kpatch list
  sudo kpatch load /usr/lib/modules/$(uname -r)/extra/kpatch/*.ko

Verification & Acceptance Criteria

All of these should pass after the fix:

rpm -q xorg-x11-server-Xwayland                                            # expected fixed NVR
sudo dnf updateinfo list cves --installed               # CVEs above no longer listed
sudo firewall-cmd --list-services
getenforce
sudo needs-restarting -r

The conditions described in the advisory must no longer be reported for xorg-x11-server-Xwayland across two consecutive runs.

Rollback Plan

Capture state before any change:

rpm -qa > /root/rpm-pre.txt
sudo dnf history list > /root/dnf-history-pre.txt
# Optional LVM snapshot of the root LV:
sudo lvcreate -s -n preupgrade -L 4G /dev/<vg>/<lv>

To revert if the patch is bad:

sudo dnf history undo <id>
# Or downgrade just the package:
sudo dnf install -y --allowerasing xorg-x11-server-Xwayland-<older-NVR>
# Or merge the LVM snapshot and reboot:
sudo lvconvert --merge /dev/<vg>/preupgrade && sudo systemctl reboot
# Custom SELinux policy cleanup:
sudo semodule -r mylocal

Prevention & Hardening

Reduce the chance of this recurring on CentOS Stream 10:

• Enable automatic security patching:

  sudo dnf install -y dnf-automatic
  sudo sed -i 's/^upgrade_type.*/upgrade_type = security/' /etc/dnf/automatic.conf
  sudo sed -i 's/^apply_updates.*/apply_updates = yes/' /etc/dnf/automatic.conf
  sudo systemctl enable --now dnf-automatic.timer

• Subscribe to centos-announce and watch Red Hat security updates for upstream changes.

• Mirror through a local Pulp / Foreman / Spacewalk-style repo for controlled rollouts:

  sudo dnf install -y dnf-utils createrepo_c
  sudo reposync --download-metadata --downloadcomps -p /srv/mirror -- repoid=baseos
  sudo createrepo_c /srv/mirror/baseos

• Version-lock sensitive packages so they cannot be auto-upgraded:

  sudo dnf install -y python3-dnf-plugin-versionlock
  sudo dnf versionlock add xorg-x11-server-Xwayland

• Monitor file integrity with AIDE:

  sudo dnf install -y aide
  sudo aide --init && sudo mv /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
  sudo aide --check

• Enable kpatch so kernel CVEs can be remediated without reboot:

  sudo dnf install -y kpatch kpatch-dnf
  sudo dnf kpatch auto
  sudo kpatch list

• Keep SELinux in enforcing mode and review custom modules in /etc/selinux/targeted/ after every package upgrade.

• Apply CIS CentOS Stream 10 Benchmark hardening and remove unused packages.

Related Errors & Cross-Refs

Issues that commonly surface alongside a xorg-x11-server-Xwayland update: dnf lock contention, systemd unit ordering cycles, SELinux AVC bursts, firewalld zone drift, and kernel taint flags. Useful triage:

sudo dnf check
systemd-analyze critical-chain
sudo ausearch -m AVC -ts today | tail
sudo firewall-cmd --get-active-zones
cat /proc/sys/kernel/tainted
sudo needs-restarting -r

View all centos-stream-10 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Primary reference: AlmaLinux/RHEL advisory ALSA-2026:11352. Manual pages useful on CentOS Stream 10:

man dnf
man dnf.conf
man systemctl
man journalctl
man firewall-cmd
man semanage
man audit2allow
man kpatch
man sosreport

Other resources: docs.centos.org, Red Hat CVE database, AlmaLinux errata, and per-package notes in /usr/share/doc/xorg-x11-server-Xwayland/ for components implicated in this advisory.