CentOS Linux 7 [TuxCare] Security Update: xorg-x11-server-Xdmx / xorg-x11-server-Xephyr / etc Multiple Vulnerabilities (CENTOS7:CLSA-2026:1790585169)

high Nessus Plugin ID 362471

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Synopsis

The CentOS Linux host is missing one or more security updates.

Description

The CentOS Linux 7 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare CENTOS7:CLSA-2026:1790585169 advisory.

- 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. (CVE-2026-33999)

- A flaw was found in the X.Org X server. This use-after-free vulnerability occurs in the XSYNC fence triggering logic, specifically within the miSyncTriggerFence() function. An attacker with access to the X11 server can exploit this without user interaction, leading to a server crash and potentially enabling memory corruption. This could result in a denial of service or further compromise of the system.
(CVE-2026-34001)

- A flaw was found in the X.Org X server's XKB key types request validation. A local attacker could send a specially crafted request to the X server, leading to an out-of-bounds memory access vulnerability. This could result in the disclosure of sensitive information or cause the server to crash, leading to a Denial of Service (DoS). In certain configurations, higher impact outcomes may be possible. (CVE-2026-34003)

- An out-of-bounds read flaw was found in the X.Org X server and Xwayland in
__glXDisp_ChangeDrawableAttributes(). A wrong size validation check can read a client-controlled number of bytes, exceeding the request buffer, leading to information disclosure. A write path also exists but requires byte-swapped clients which is disabled by default. (CVE-2026-50262)

- A use-after-free flaw was found in the X.Org X server and Xwayland in CreateSaverWindow(). A client can trigger a use-after-free read after changing window attributes and forcing the screen saver, leading to information disclosure. (CVE-2026-50263)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Update the affected packages based on the guidance in TuxCare advisory CENTOS7:CLSA-2026:1790585169.

Plugin Details

Severity: High

ID: 362471

File Name: tuxcare_centos_7_CLSA-2026-1790585169.nasl

Version: 1.3

Type: Local

Agent: unix

Family: CentOS Local Security Checks

Published: 10/1/2026

Updated: 10/17/2026

Supported Sensors: Nessus Agent, Continuous Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.9

Percentile: 96.42

Vendor

Vendor Severity: Moderate

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5

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

CVSS Score Source: CVE-2026-55999

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.8

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:O/RC:C

Vulnerability Information

Required KB Items: Host/local_checks_enabled, Host/CentOS/release, Host/CentOS/rpm-list, Host/OS/extended-third-party

Exploit Ease: No known exploits are available

Patch Publication Date: 9/28/2026

Vulnerability Publication Date: 6/1/2026

Reference Information

CVE: CVE-2026-33999, CVE-2026-34001, CVE-2026-34003, CVE-2026-50262, CVE-2026-50263, CVE-2026-55999

CLSA: 2026:1790585169

Detections

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