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X.Org Server CVE-2026-33999

| EUVDEUVD-2026-25229 HIGH
Integer Underflow (CWE-191)
2026-04-23 redhat GHSA-g562-3mh5-27v6
7.8
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
7.1 HIGH

Requires an authorized local/X11 client connection (AV:L, PR:L, AC:L); a read overrun leaks server memory (C:H) and crashes the server (A:H) but does not clearly enable writes (I:N).

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
HIGH
qualitative
Red Hat
7.8 HIGH
qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
Analysis Generated
Jul 24, 2026 - 04:45 vuln.today
Patch released
Apr 28, 2026 - 20:30 nvd
Patch available
EUVD ID Assigned
Apr 23, 2026 - 16:00 euvd
EUVD-2026-25229
CVE Published
Apr 23, 2026 - 14:53 nvd
HIGH 7.8

DescriptionCVE.org

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.

AnalysisAI

Memory-disclosure and denial-of-service in the X.Org X server arises from an integer underflow (CWE-191) in the XKB compatibility map handling, which lets a client with local or remote X11 access trigger an out-of-bounds buffer read. Any attacker able to open a connection to the display server can crash it or read adjacent server memory, with Red Hat and SUSE rating the technical impact as total; no public exploit identified at time of analysis and EPSS is negligible (0.01%, 2nd percentile). This was reported by Red Hat and affects the X server shipped across Red Hat Enterprise Linux 6 through 10.

Technical ContextAI

The X.Org Server is the reference implementation of the X11 display server that mediates between client applications and graphics/input hardware on most Linux and BSD desktops. The flaw lives in the XKB (X Keyboard Extension) subsystem, specifically the routines that parse and store compatibility maps (compat map) sent via XKB protocol requests. CWE-191 (integer underflow) indicates a size or count value is decremented below zero (or a subtraction wraps around on an unsigned type), producing a huge or invalid length that is then used as a bound for a read operation, causing the server to read past the end of an allocated buffer. Because a single X server process handles all connected clients with elevated access to input and framebuffer state, out-of-bounds reads in this code path can leak server-process memory to the malicious client or corrupt internal state enough to crash the server.

RemediationAI

Patch available per vendor advisory: apply the updated xorg-x11-server packages from your distribution and restart the X session (or reboot). Red Hat provides fixes via errata RHSA-2026:10739, RHSA-2026:11352, and RHSA-2026:11369 (https://access.redhat.com/errata/RHSA-2026:10739); SUSE publishes fixes in SUSE-SU-2026:1328 through 1335 and SUSE-SU-2026:21211 (https://www.suse.com/support/update/SUSE-SU-2026:1328/). Exact fixed package versions are enumerated in those errata and should be pulled directly rather than guessed. If patching must be deferred, reduce exposure by restricting who can connect to the display server: keep X access authorization enabled (never run 'xhost +'), disable remote TCP listening on the X server (the '-nolisten tcp' default) so only local authorized clients can reach it, and on multi-user hosts limit local login/console access - the trade-off is that legitimate remote X11 or multi-seat use cases will break. Migrating GUI workloads to Wayland where feasible removes this X-server code path entirely, at the cost of application compatibility testing.

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Vendor StatusVendor

SUSE

Severity: High
Product Status
Image SLES15-SP4-SAP Image SLES15-SP4-SAP-Azure Image SLES15-SP4-SAP-EC2 Image SLES15-SP4-SAP-GCE Image SLES15-SP4-SAPCAL Image SLES15-SP4-SAPCAL-Azure Image SLES15-SP4-SAPCAL-EC2 Image SLES15-SP4-SAPCAL-GCE Affected
Image SLES15-SP5-SAPCAL-Azure Image SLES15-SP5-SAPCAL-GCE Affected
Image SLES15-SP6-SAP Image SLES15-SP6-SAP-EC2 Image SLES15-SP6-SAPCAL Image SLES15-SP6-SAPCAL-EC2 Affected
SUSE Liberty Linux 9 Fixed
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

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CVE-2026-33999 vulnerability details – vuln.today

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