HIGH

CVE-2026-55999

CVSS v3

8.5

HIGH

EPSS Score

0.3 %

exploit probability, as of 2026-10-19

CISA KEV

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

xorg-x11-server-XdmxAlmaLinux:9all versions · fixed in 1.20.11-34.el9_8.3and 7 other packages
xorg-x11-server-XdmxAlmaLinux:8all versions · fixed in 1.20.11-28.el8_10.3and 7 other packages
xorg-x11-server-XwaylandAlmaLinux:10all versions · fixed in 24.1.9-4.el10_2.3and 1 other package
xorg-x11-server-XwaylandAlmaLinux:9all versions · fixed in 24.1.9-4.el9_8.3and 1 other package
xorg-x11-server-XwaylandAlmaLinux:8all versions · fixed in 21.1.3-20.el8_10.3

Vendor advisories

CVE-2026-55999 Red Hat Product Security699 products fixed
xorg: X11: xserver: X.org: glamor Font Atlas Heap Buffer Overflow
RHSA-2026:53450 Red Hat Product Security8 products fixed
Red Hat Security Advisory: xorg-x11-server-Xwayland security update
RHSA-2026:52398 Red Hat Product Security13 products fixed
Red Hat Security Advisory: xorg-x11-server-Xwayland security update
RHSA-2026:52397 Red Hat Product Security13 products fixed
Red Hat Security Advisory: xorg-x11-server-Xwayland security update
RHSA-2026:52392 Red Hat Product Security11 products fixed
Red Hat Security Advisory: xorg-x11-server-Xwayland security update
RHSA-2026:50718 Red Hat Product Security29 products fixed
Red Hat Security Advisory: xorg-x11-server-Xwayland security update

13 more advisories

Full record on NVD

Description

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.

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Published: 2026-07-08
Last Modified: 2026-07-09

Frequently asked questions

What is CVE-2026-55999?

Is CVE-2026-55999 actively exploited?

Active exploitation of CVE-2026-55999 has not been confirmed. Its EPSS score was 0.3% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-55999?

CVE-2026-55999 has a CVSS v3 base score of 8.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H.

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