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CVE-2026-8863 Microsoft CVE debrief

CVE-2026-8863 is a HIGH severity vulnerability with a CVSS score of 7.8. Multiple Microsoft-signed UEFI SHIM bootloaders are vulnerable to SecureBoot bypass. An attacker with administrative privileges or the ability to modify the boot process could use one of the vulnerable shim bootloaders to bypass Secure Boot protections and execute arbitrary code before the operating system loads. A specific UEFI DBX update is required to block these vulnerable boot loaders.

Vendor
Microsoft
Product
UEFI SHIM bootloader
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-09
Original CVE updated
2026-06-09
Advisory published
2026-06-09
Advisory updated
2026-06-09

Who should care

Administrators and users of systems with UEFI Secure Boot enabled should be aware of this vulnerability. Specifically, those with Microsoft-signed UEFI SHIM bootloaders may be affected.

Technical summary

The vulnerability exists in multiple Microsoft-signed UEFI SHIM bootloaders, allowing an attacker with administrative privileges or the ability to modify the boot process to bypass Secure Boot protections. This could enable the execution of arbitrary code before the operating system loads.

Defensive priority

High

Recommended defensive actions

  • Apply the specific UEFI DBX update to block the vulnerable boot loaders.
  • Ensure that Secure Boot is enabled and properly configured.
  • Restrict access to the boot process to prevent modifications by unauthorized users.

Evidence notes

The CVE record and NVD detail provide official information about this vulnerability. Additional details can be found in the CERT and Microsoft advisories.

Official resources

CVE-2026-8863 was published on 2026-06-09T19:17:59.210Z and modified on 2026-06-09T21:17:26.447Z.