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

highCVSS 8.5CVE-2026-55999

CSIRTS triage

vendor: X.Org product: xorg-server Memory corruption

What: There is a heap buffer overflow in the glamor font atlas.
Who is affected: Deployments of xorg-server are affected.
Urgency: Remediation is urgent due to the high severity and potential for exploitation.
Action: Update to the latest version of xorg-server.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 8.5
Published: 2026-07-02
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55999

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-559990.21% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 11% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55999	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for xorg-server / xwayland

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-56000: Local attackers with a X connection able to provide GLX commit to the X server xorg-server bef…nvd · 2026-07-08
highCVE-2026-55999: Local attackers with a X connection able to provide PCX fonts to the X server xorg-server befo…nvd · 2026-07-08