CVE-2026-8863: UEFI Secure Boot Security Feature Bypass Vulnerability

highCVSS 7.8CVE-2026-8863

Protection mechanism failure in Windows UEFI allows an authorized attacker to bypass a security feature locally.

CSIRTS triage

vendor: Microsoft product: Windows UEFIOther

What: A protection mechanism failure allows an authorized attacker to bypass a security feature locally.
Who is affected: Deployments of Windows UEFI.
Urgency: Remediation is urgent due to the high severity of the vulnerability.
Action: Implement security measures to mitigate the bypass risk.

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 7.8
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-8863

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-2026-88630.10% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 1% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-8863	coverage & exploitation status	NVD · CVE.org

Recent advisories for UEFI Secure Boot

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-2026-45656: UEFI Secure Boot Security Feature Bypass Vulnerabilitymsrc · 2026-06-09