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Fencer Intel
high 8.5

CVE-2026-55999 json

xorg-server / xwayland glamor font atlas Heap Buffer Overflow

published 4mo ago modified 4mo ago also EUVD-2026-42188

cvss
8.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 26%
public exploits
0
none known

Summary

Local attackers with a X connection able to provide PCX fonts to the X server xorg-server before 21.2.24 and xwayland before 24.1.13 could cause a heap buffer overflow via SetFont due to missing glyph boundary checks.

Patch / fix

  • X.Org xorg-server 21.1.24
  • X.Org xwayland 24.1.13
  • xwayland Debian 14 2:24.1.13-1
  • xorg-server Debian 13 2:21.1.16-1.3+deb13u4
  • xorg-server Debian 14 2:21.1.24-1

debian advisories DEBIAN-CVE-2026-55999

  • xorg-x11-server-Xwayland RHEL 9 24.1.9-4.el9_8.3
  • xorg-x11-server-Xwayland RHEL 10.2 24.1.9-4.el10_2.3
  • xorg-x11-server RHEL 8 1.20.11-28.el8_10.3
  • xorg-x11-server-Xdmx RHEL 8 1.20.11-28.el8_10.3
  • xorg-x11-server-Xorg RHEL 8 1.20.11-28.el8_10.3
  • xorg-x11-server-Xvfb RHEL 8 1.20.11-28.el8_10.3
  • xorg-x11-server-Xnest RHEL 8 1.20.11-28.el8_10.3
  • xorg-x11-server-common RHEL 8 1.20.11-28.el8_10.3

red hat advisories RHSA-2026:53450RHSA-2026:52398RHSA-2026:52397RHSA-2026:52392RHSA-2026:50718RHSA-2026:50116

  • xwayland SLES for SAP applications 16.0, SLES 16.0 24.1.6-160000.6.1
  • xorg-x11-server SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 21.1.4-150500.7.52.1
  • xorg-x11-server SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE High Performance Computing 15 SP4-LTSS +1 more 1.20.3-150400.38.74.1
  • xorg-x11-server SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 21.1.15-150700.5.22.1
  • xwayland SLE Workstation Extension 15 SP7 24.1.5-150700.3.22.1
  • xorg-x11-server SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 1.19.6-10.105.1
  • xorg-x11-server SLES for SAP 15 SP6, SLES 15 SP6-LTSS 21.1.11-150600.5.31.1

suse advisories SUSE-SU-2026:22617-1SUSE-SU-2026:2792-1SUSE-SU-2026:2791-1SUSE-SU-2026:2789-1SUSE-SU-2026:2788-1SUSE-SU-2026:2787-1

  • xwayland openSUSE Leap 16.0 24.1.6-160000.6.1
  • xorg-x11-server openSUSE Tumbleweed 21.1.21-8.1
  • xorg-x11-server openSUSE Leap 16.0 21.1.15-160000.6.1
  • xwayland openSUSE Tumbleweed 24.1.12-1.1

opensuse advisories openSUSE-SU-2026:21283-1openSUSE-SU-2026:11244-1openSUSE-SU-2026:21273-1openSUSE-SU-2026:11227-1

  • xorg-x11-server-Xdmx AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-Xorg AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-Xvfb AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-Xnest AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-common AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-source AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-Xephyr AlmaLinux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-Xdmx AlmaLinux 8 1.20.11-28.el8_10.3

almalinux advisories ALSA-2026:38486ALSA-2026:38487ALSA-2026:38488ALSA-2026:38489ALSA-2026:38490

  • xorg-x11-server-Xwayland Rocky Linux 10 24.1.9-4.el10_2.3
  • xorg-x11-server Rocky Linux 9 1.20.11-34.el9_8.3
  • xorg-x11-server-Xwayland Rocky Linux 9 24.1.9-4.el9_8.3
  • xorg-x11-server Rocky Linux 8 1.20.11-28.el8_10.3
  • xorg-x11-server-Xwayland Rocky Linux 8 21.1.3-20.el8_10.3

rocky linux advisories RLSA-2026:38489RLSA-2026:38486RLSA-2026:38490RLSA-2026:38487RLSA-2026:38488

  • xwayland Alpine 3.24 24.1.13-r0
  • xorg-server Alpine 3.24 21.1.24-r0

alpine advisories ALPINE-CVE-2026-55999

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-55999 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-55999 updated cvss 7.5

xorg: X11: xserver: X.org: glamor Font Atlas Heap Buffer Overflow

  • Red Hat CodeReady Linux Builder EUS (v.9.6) xorg-x11-server-source 1.20.11-34.el9_6.1, xorg-x11-server-Xwayland 23.2.7-6.el9_6.3
    fixed: vendor fix RHSA-2026:49608
  • Red Hat Enterprise Linux AppStream (v. 8) xorg-x11-server 1.20.11-28.el8_10.3, xorg-x11-server-Xdmx 1.20.11-28.el8_10.3, xorg-x11-server-Xorg 1.20.11-28.el8_10.3, xorg-x11-server-Xvfb 1.20.11-28.el8_10.3, xorg-x11-server-Xnest 1.20.11-28.el8_10.3, xorg-x11-server-common 1.20.11-28.el8_10.3, +2 more
    fixed: vendor fix RHSA-2026:38487
  • Red Hat Enterprise Linux AppStream (v. 9) xorg-x11-server 1.20.11-34.el9_8.3, xorg-x11-server-Xdmx 1.20.11-34.el9_8.3, xorg-x11-server-Xorg 1.20.11-34.el9_8.3, xorg-x11-server-Xvfb 1.20.11-34.el9_8.3, xorg-x11-server-Xnest 1.20.11-34.el9_8.3, xorg-x11-server-common 1.20.11-34.el9_8.3, +2 more
    fixed: vendor fix RHSA-2026:38486
  • Red Hat Enterprise Linux AppStream (v. 10) xorg-x11-server-Xwayland 24.1.9-4.el10_2.3
    fixed: vendor fix RHSA-2026:38489
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) xorg-x11-server 1.20.10-5.el8_4.1, xorg-x11-server-Xdmx 1.20.10-5.el8_4.1, xorg-x11-server-Xorg 1.20.10-5.el8_4.1, xorg-x11-server-Xvfb 1.20.10-5.el8_4.1, xorg-x11-server-Xnest 1.20.10-5.el8_4.1, xorg-x11-server-common 1.20.10-5.el8_4.1, +2 more
    fixed: vendor fix RHSA-2026:49606
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) xorg-x11-server 1.20.11-8.el8_6.1, xorg-x11-server-Xdmx 1.20.11-8.el8_6.1, xorg-x11-server-Xorg 1.20.11-8.el8_6.1, xorg-x11-server-Xvfb 1.20.11-8.el8_6.1, xorg-x11-server-Xnest 1.20.11-8.el8_6.1, xorg-x11-server-common 1.20.11-8.el8_6.1, +2 more
    fixed: vendor fix RHSA-2026:49605
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) xorg-x11-server 1.20.11-19.el8_8.1, xorg-x11-server-Xdmx 1.20.11-19.el8_8.1, xorg-x11-server-Xorg 1.20.11-19.el8_8.1, xorg-x11-server-Xvfb 1.20.11-19.el8_8.1, xorg-x11-server-Xnest 1.20.11-19.el8_8.1, xorg-x11-server-common 1.20.11-19.el8_8.1, +2 more
    fixed: vendor fix RHSA-2026:50116
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) xorg-x11-server 1.20.11-21.el9_2.1, xorg-x11-server-Xdmx 1.20.11-21.el9_2.1, xorg-x11-server-Xorg 1.20.11-21.el9_2.1, xorg-x11-server-Xvfb 1.20.11-21.el9_2.1, xorg-x11-server-Xnest 1.20.11-21.el9_2.1, xorg-x11-server-common 1.20.11-21.el9_2.1, +2 more
    fixed: vendor fix RHSA-2026:49515
show 12 more
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) xorg-x11-server 1.20.11-29.el9_4.1, xorg-x11-server-Xdmx 1.20.11-29.el9_4.1, xorg-x11-server-Xorg 1.20.11-29.el9_4.1, xorg-x11-server-Xvfb 1.20.11-29.el9_4.1, xorg-x11-server-Xnest 1.20.11-29.el9_4.1, xorg-x11-server-common 1.20.11-29.el9_4.1, +2 more
    fixed: vendor fix RHSA-2026:49516
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) xorg-x11-server-Xwayland 24.1.5-6.el10_0.2
    fixed: vendor fix RHSA-2026:50100
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) xorg-x11-server 1.20.11-34.el9_6.1, xorg-x11-server-Xdmx 1.20.11-34.el9_6.1, xorg-x11-server-Xorg 1.20.11-34.el9_6.1, xorg-x11-server-Xvfb 1.20.11-34.el9_6.1, xorg-x11-server-Xnest 1.20.11-34.el9_6.1, xorg-x11-server-common 1.20.11-34.el9_6.1, +2 more
    fixed: vendor fix RHSA-2026:49608
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) xorg-x11-server 1.20.10-5.el8_4.1, xorg-x11-server-Xdmx 1.20.10-5.el8_4.1, xorg-x11-server-Xorg 1.20.10-5.el8_4.1, xorg-x11-server-Xvfb 1.20.10-5.el8_4.1, xorg-x11-server-Xnest 1.20.10-5.el8_4.1, xorg-x11-server-common 1.20.10-5.el8_4.1, +2 more
    fixed: vendor fix RHSA-2026:49606
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) xorg-x11-server 1.20.11-8.el8_6.1, xorg-x11-server-Xdmx 1.20.11-8.el8_6.1, xorg-x11-server-Xorg 1.20.11-8.el8_6.1, xorg-x11-server-Xvfb 1.20.11-8.el8_6.1, xorg-x11-server-Xnest 1.20.11-8.el8_6.1, xorg-x11-server-common 1.20.11-8.el8_6.1, +2 more
    fixed: vendor fix RHSA-2026:49605
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) xorg-x11-server 1.20.11-19.el8_8.1, xorg-x11-server-Xdmx 1.20.11-19.el8_8.1, xorg-x11-server-Xorg 1.20.11-19.el8_8.1, xorg-x11-server-Xvfb 1.20.11-19.el8_8.1, xorg-x11-server-Xnest 1.20.11-19.el8_8.1, xorg-x11-server-common 1.20.11-19.el8_8.1, +2 more
    fixed: vendor fix RHSA-2026:50116
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) xorg-x11-server-source 1.20.11-34.el9_8.3, xorg-x11-server-Xwayland 24.1.9-4.el9_8.3
    fixed: vendor fix RHSA-2026:38486
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) xorg-x11-server-Xwayland-devel 24.1.9-4.el10_2.3, xorg-x11-server-Xwayland-debuginfo 24.1.9-4.el10_2.3, xorg-x11-server-Xwayland-debugsource 24.1.9-4.el10_2.3
    fixed: vendor fix RHSA-2026:38489
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) xorg-x11-server-Xwayland-devel 24.1.5-6.el10_0.2, xorg-x11-server-Xwayland-debuginfo 24.1.5-6.el10_0.2, xorg-x11-server-Xwayland-debugsource 24.1.5-6.el10_0.2
    fixed: vendor fix RHSA-2026:50100
  • Red Hat Enterprise Linux CRB (v. 8) xorg-x11-server-source 1.20.11-28.el8_10.3
    fixed: vendor fix RHSA-2026:38487
  • Red Hat Enterprise Linux Server (v. 7 ELS) xorg-x11-server 1.20.4-36.el7_9, xorg-x11-server-Xorg 1.20.4-36.el7_9, xorg-x11-server-common 1.20.4-36.el7_9, xorg-x11-server-Xephyr 1.20.4-36.el7_9 Red Hat Enterprise Linux Server Optional (v. 7 ELS) xorg-x11-server-Xdmx 1.20.4-36.el7_9, xorg-x11-server-Xvfb 1.20.4-36.el7_9, xorg-x11-server-Xnest 1.20.4-36.el7_9, xorg-x11-server-source 1.20.4-36.el7_9, xorg-x11-server-Xwayland 1.20.4-36.el7_9
    fixed: vendor fix RHSA-2026:50117
  • Red Hat Enterprise Linux 6 xorg-x11-server, xorg-x11-server-Xdmx, xorg-x11-server-Xorg, xorg-x11-server-Xvfb, xorg-x11-server-Xnest, xorg-x11-server-common, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
4mo ago

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 26% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 8.5 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • X.Org xorg-server
  • X.Org xwayland

Classification

Weakness
  • CWE-122 Heap-based Buffer Overflow

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.