CVE-2026-33999

Xorg: xwayland: x.org x server: denial of service via integer underflow in xkb compatibility map handling

Published Apr 23, 2026 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed
Description
A flaw was found in the X.Org X server. This integer underflow vulnerability, specifically in the XKB compatibility map handling, allows an attacker with local or remote X11 server access to trigger a buffer read overrun. This can lead to memory-safety violations and potentially a denial of service (DoS) or other severe impacts.

Remediation

Vendor Workaround

To mitigate this issue, restrict access to the X11 server. For remote access, disable X11 forwarding in SSH configurations if not required. Edit `/etc/ssh/sshd_config` and set `X11Forwarding no`. After modifying the configuration, restart the `sshd` service using `systemctl restart sshd`. Disabling X11 forwarding may impact remote graphical applications.

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4738-1 xorg-server security update
References
Link Providers
https://access.redhat.com/errata/RHSA-2026:10739 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:11352 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:11369 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:11388 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:11656 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:11692 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:13414 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:19125 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:19342 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:19343 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:19344 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20547 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20555 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20557 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20558 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20560 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20561 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20562 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20563 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20575 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20576 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:20590 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21699 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21712 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21715 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21716 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21718 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21741 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:21742 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:22424 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:22456 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:23254 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:23255 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:23496 cve-icon cve-icon
https://access.redhat.com/errata/RHSA-2026:24341 cve-icon cve-icon
https://access.redhat.com/security/cve/CVE-2026-33999 cve-icon cve-icon
https://bugzilla.redhat.com/show_bug.cgi?id=2451106 cve-icon cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2026-33999 cve-icon
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33999.json cve-icon
https://www.cve.org/CVERecord?id=CVE-2026-33999 cve-icon
History
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:6
Type Values Removed Values Added
CPEs cpe:/a:redhat:rhel_eus_long_life:8.6::appstream
References
Type Values Removed Values Added
First Time appeared Redhat rhel Eus Long Life
CPEs cpe:/a:redhat:rhel_aus:8.4::appstream
cpe:/a:redhat:rhel_eus_long_life:8.4::appstream
Vendors & Products Redhat rhel Eus Long Life
References
Type Values Removed Values Added
First Time appeared Redhat rhel Aus
Redhat rhel Tus
CPEs cpe:/a:redhat:rhel_aus:8.6::appstream
cpe:/a:redhat:rhel_e4s:8.6::appstream
cpe:/a:redhat:rhel_e4s:8.8::appstream
cpe:/a:redhat:rhel_tus:8.6::appstream
cpe:/a:redhat:rhel_tus:8.8::appstream
Vendors & Products Redhat rhel Aus
Redhat rhel Tus
References
Type Values Removed Values Added
First Time appeared Redhat enterprise Linux Eus
Redhat rhel Els
CPEs cpe:/a:redhat:rhel_eus:9.6::appstream
cpe:/a:redhat:rhel_eus:9.6::crb
cpe:/o:redhat:enterprise_linux_eus:10.0
cpe:/o:redhat:rhel_els:7
Vendors & Products Redhat enterprise Linux Eus
Redhat rhel Els
References
Type Values Removed Values Added
First Time appeared Redhat rhel Eus
CPEs cpe:/a:redhat:rhel_eus:9.4::appstream
Vendors & Products Redhat rhel Eus
References
Type Values Removed Values Added
First Time appeared Redhat rhel E4s
CPEs cpe:/a:redhat:rhel_e4s:9.0::appstream
Vendors & Products Redhat rhel E4s
References
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:10.2
References
Type Values Removed Values Added
CPEs cpe:/a:redhat:enterprise_linux:8::appstream
cpe:/a:redhat:enterprise_linux:8::crb
References
Type Values Removed Values Added
CPEs cpe:/a:redhat:enterprise_linux:9::crb
References
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:10 cpe:/o:redhat:enterprise_linux:10.1
References
Type Values Removed Values Added
CPEs cpe:/a:redhat:enterprise_linux:9::appstream
References
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description A flaw was found in the X.Org X server. This integer underflow vulnerability, specifically in the XKB compatibility map handling, allows an attacker with local or remote X11 server access to trigger a buffer read overrun. This can lead to memory-safety violations and potentially a denial of service (DoS) or other severe impacts.
Title Xorg: xwayland: x.org x server: denial of service via integer underflow in xkb compatibility map handling
First Time appeared Redhat
Redhat enterprise Linux
Weaknesses CWE-191
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
References
Metrics cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
redhat
Published
Updated
Nov 4, 2026, 10:25 PM
Reserved
Mar 25, 2026, 4:53 AM
Status
Awaiting Analysis
Published
Apr 23, 2026, 4:16 PM
Modified
Nov 4, 2026, 11:17 PM
Severity
Important
Public date
Apr 23, 2026, 2:11 PM