Buffer overflow in X.org Xorg-Server
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 xwayland before 24.1.13 could cause a heap buffer overflow via SetFont due to missing glyph boundary checks.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.003 (24.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 24th percentile — 24.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.001
Affected products
- X.org Xorg-Server — versions 0
- X.org X Server
- X.org Xwayland — versions 0
Weakness classification (CWE)
References
- gitlab.freedesktop.org/xorg/xserver/-/commit/fbf7bac22e2c6bd627fb042742a2331826… (Patch, patch)
- www.openwall.com/lists/oss-security/2026/07/08/2 (vendor-advisory, Patch, Mailing List, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-55999?
- CVE-2026-55999 is a high-severity vulnerability in X.org Xorg-Server, classified under Heap-based Buffer Overflow. CVSS score: 8.5/10. Published 2026-07-08.
- How severe is CVE-2026-55999?
- High severity. CVSS v3 base score is 8.5 out of 10.