CVE-2026-55999
Heap overflow in xorg-server/xwayland font handling via PCX fonts
Is CVE-2026-55999 being exploited?
Not confirmed. CVE-2026-55999 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.27% probability of exploitation in the next 30 days.
How severe is CVE-2026-55999?
CVE-2026-55999 is rated High with a CVSS score of 8.5. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-55999?
Yes. A fix has been recorded for CVE-2026-55999. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-55999 affect?
CVE-2026-55999 affects xorg-server < 21.2.24, xwayland < 24.1.13, Linux desktops/servers running X11/XWayland. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-55999?
Upgrade xorg-server to >=21.2.24 and xwayland to >=24.1.13
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Local attacker with X connection can trigger heap overflow via SetFont, causing crashes or possible arbitrary code execution and local privilege escalation.
Patch when possible
- affected< 21.1.24
- affected< 24.1.13
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.