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

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-08 · updated 2026-07-09
Weakness: CWE-122

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.

Affected products

xorg-x11-server: before 21.2.24 — fixed in 21.2.24
X.Org xwayland: before 24.1.13 — fixed in 24.1.13

How to fix

Upgrade to a fixed version: xorg-x11-server 21.2.24; X.Org xwayland 24.1.13. Check the vendor advisory for mitigations.

References

https://gitlab.freedesktop.org/xorg/xserver/-/commit/fbf7bac22e2c6bd627fb042742a23318263edae1
https://www.openwall.com/lists/oss-security/2026/07/08/2

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