Debian dla-4737 : xnest - security update

high Nessus Plugin ID 335005

Synopsis

The remote Debian host is missing one or more security-related updates.

Description

The remote Debian 12 host has packages installed that are affected by multiple vulnerabilities as referenced in the dla-4737 advisory.

- ------------------------------------------------------------------------- Debian LTS Advisory DLA-4737-1 [email protected] https://www.debian.org/lts/security/ Arnaud Rebillout August 13, 2026 https://wiki.debian.org/LTS
- -------------------------------------------------------------------------

Package : xorg-server Version : 2:21.1.7-3+deb12u13 CVE ID : CVE-2022-49737 CVE-2026-50256 CVE-2026-50257 CVE-2026-50258 CVE-2026-50259 CVE-2026-50260 CVE-2026-50261 CVE-2026-50262 CVE-2026-50263 CVE-2026-50264 Debian Bug : 1081338 1138680

Several vulnerabilities were discovered in the Xorg X server, which may result in privilege escalation if the X server is running privileged.

CVE-2022-49737

In X.Org X server 20.11 through 21.1.16, when a client application uses easystroke for mouse gestures, the main thread modifies various data structures used by the input thread without acquiring a lock, aka a race condition. In particular, AttachDevice in dix/devices.c does not acquire an input lock.

CVE-2026-50256

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.

CVE-2026-50257

A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDestroyFence(). A client that sets up multiple fence triggers can trigger a use-after-free function pointer call. An attacker would connect to the X server to set up a fence and await that fence, then a second X connection destroys the fence, causing the use-after-free.
This may be used to crash the server, or for privilege escalation if the X server runs as root.

CVE-2026-50258

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. The X server has multiple stack buffers sized XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify or clamp non-canonical key types to XkbMaxShiftLevel. A client can change key types to excessive shift levels and trigger stack overflows. This is caused by an incomplete fix of CVE-2025-26597.
This may be used to crash the server, or for privilege escalation if the X server runs as root.

CVE-2026-50259

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. _XkbSetMapChecks() declares a fixed-size stack buffer mapWidths[256] indexed by key type index. The helper function CheckKeyTypes() writes to this buffer at a client-controlled offset, allowing a stack buffer overflow. This may be used to crash the server, or for privilege escalation if the X server runs as root.

CVE-2026-50260

A use-after-free flaw was found in the X.Org X server and Xwayland in FreeCounter(). A client that sets up multiple SyncCounters and awaits on those triggers can trigger a use-after-free when destroying those counters via a second client connection. This may be used to crash the server, or for privilege escalation if the X server runs as root.

CVE-2026-50261

A use-after-free flaw was found in the X.Org X server and Xwayland in SyncChangeCounter(). A client that sets up multiple SyncCounters can trigger a use-after-free when destroying those counters via a second client connection while changing those counters. This may be used to crash the server, or for privilege escalation if the X server runs as root.

CVE-2026-50262

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-2026-50263

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-2026-50264

An out-of-bounds write flaw was found in the X.Org X server and Xwayland in DRIGetBuffers/DRIGetBuffersWithFormat. A client that requests multiple DRI2BufferBackLeft attachments and one DRI2BufferFrontLeft can trigger an out-of-bounds heap write. This may be used to crash the server, or for privilege escalation if the X server runs as root.

For Debian 12 bookworm, these problems have been fixed in version 2:21.1.7-3+deb12u13.

We recommend that you upgrade your xorg-server packages.

For the detailed security status of xorg-server please refer to its security tracker page at:
https://security-tracker.debian.org/tracker/xorg-server

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS

Tenable has extracted the preceding description block directly from the Debian security advisory.

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

Solution

Upgrade the xnest packages.

Plugin Details

Severity: High

ID: 335005

File Name: debian_DLA-4737.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Debian Local Security Checks

Published: 8/13/2026

Updated: 8/13/2026

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

Risk Information

VPR

Risk Factor: High

Score: 7.6

Percentile: 98.4

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-2025-26597

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

CPE: cpe:/o:debian:debian_linux:12.0, p-cpe:/a:debian:debian_linux:xnest, p-cpe:/a:debian:debian_linux:xorg-server-source, p-cpe:/a:debian:debian_linux:xserver-common, p-cpe:/a:debian:debian_linux:xserver-xephyr, p-cpe:/a:debian:debian_linux:xserver-xorg-core-udeb, p-cpe:/a:debian:debian_linux:xserver-xorg-core, p-cpe:/a:debian:debian_linux:xserver-xorg-dev, p-cpe:/a:debian:debian_linux:xserver-xorg-legacy, p-cpe:/a:debian:debian_linux:xvfb

Required KB Items: Host/local_checks_enabled, Host/Debian/release, Host/Debian/dpkg-l

Exploit Ease: No known exploits are available

Patch Publication Date: 8/13/2026

Vulnerability Publication Date: 2/25/2025

Reference Information

CVE: CVE-2022-49737, CVE-2025-26597, CVE-2026-50256, CVE-2026-50257, CVE-2026-50258, CVE-2026-50259, CVE-2026-50260, CVE-2026-50261, CVE-2026-50262, CVE-2026-50263, CVE-2026-50264

Detections

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