CVE-2026-55999: Local attackers with a X connection able to provide PCX fonts to the X server xorg-server before 21.2.24 and

Q: How do I fix CVE-2026-55999?

x server: upgrade to 21.2.24; xwayland: upgrade to 24.1.13. Exact commands for each OS are on this page.

Q: Is CVE-2026-55999 being exploited?

CVE-2026-55999 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-55999 affect?

CVE-2026-55999 affects x server, xwayland. Severity is high (CVSS 8.5). 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.

Routine

HIGH 8.5UPGRADEUPGRADE

CVE-2026-55999 is a high-severity flaw (CVSS 8.5) affecting x server, xwayland. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	8.5 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 74%)
CISA exploited list	No
Weakness	CWE-122
Published	2026-07-08
Last modified	2026-07-09

Publisher (CNA): SUSE · Vendor: x.org

Last updated 2026-07-09 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-08 09:16 UTCPublished CVE record published
2026-07-09 19:49 UTCUpdated Record last modified

x.org x server UPGRADE

Affected: < 21.2.24

Fixed in: 21.2.24

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy x-server || rpm -q x-server || x-server --version

2. UPGRADE to 21.2.24 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade x-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade x-server

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

x.org xwayland UPGRADE

Affected: < 24.1.13

Fixed in: 24.1.13

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy xwayland || rpm -q xwayland || xwayland --version

2. UPGRADE to 24.1.13 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade xwayland

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade xwayland

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:38486] Important: xorg-x11-server security update 2026-07-14

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-55999?

x server: upgrade to 21.2.24; xwayland: upgrade to 24.1.13. Exact commands for each OS are on this page.

Is CVE-2026-55999 being exploited?

CVE-2026-55999 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-55999 affect?

CVE-2026-55999 affects x server, xwayland. Severity is high (CVSS 8.5). 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.

How urgent is CVE-2026-55999?

Priority 36/100. High severity

Related CVEs

CVE-2026-34000 MEDIUM 6.1 MITIGATE MITIGATE A flaw was found in the X.Org X server
CVE-2026-34002 MEDIUM 6.1 MITIGATE MITIGATE A flaw was found in the X.Org X server
CVE-2026-50261 HIGH 7.8 UPGRADE UPGRADE A use-after-free flaw was found in the X.Org X server and Xwayland in SyncChangeCounter()
CVE-2026-50260 HIGH 7.8 UPGRADE UPGRADE A use-after-free flaw was found in the X.Org X server and Xwayland in FreeCounter()
CVE-2026-50259 HIGH 7.8 UPGRADE UPGRADE A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland

References

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