CVE-2026-55999: xorg-server / xwayland glamor font atlas Heap Buffer Overflow

High severity · published Jul 8, 2026

CVE-2026-55999

xorg-server / xwayland glamor font atlas Heap Buffer Overflow

7.8

CVSS

0.3%

EPSS

On KEV

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.

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack vector

Local

Complexity

Low

Privileges

Low

User interaction

None

Confidentiality

High

Integrity

High

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.3% · higher than 26% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

xorg-server · X.Org

before 21.1.24 · source: vendor

xwayland · X.Org

before 24.1.13 · source: vendor, NVD

X Server · X.org

before 21.2.24 · source: NVD

In the news

VulnerabilityHigh

ZDI-26-409: X.Org Server Glamor Font Heap-based Buffer Overflow Privilege Escalation Vulnerability

This vulnerability allows local attackers to escalate privileges on affected installations of X.Org Server. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability. The ZDI has assigned a CVSS rating of 7.8. The following CVEs are assigned: CVE-2026-55999.

CVE-2026-55999

Jul 15, 2026·Zero Day Initiative

Affected product

xorg-server

X.Org

All xorg-server CVEs

References

NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-55999

CVE.org

https://www.cve.org/CVERecord?id=CVE-2026-55999

Patch

https://gitlab.freedesktop.org/xorg/xserver/-/commit/fbf7bac22e2c6bd627fb042742a23318263edae1

Mailing List

https://www.openwall.com/lists/oss-security/2026/07/08/2