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Date: Thu, 22 Sep 2016 07:58:47 -0400 (EDT)
From: Vladis Dronov <>
Subject: kernel: ACPI table override is allowed when securelevel is enabled


A vulnerability was found in the RHEL7 kernel. When RHEL7 is booted with UEFI Secure Boot enabled,
securelevel is set. The kernel uses the state of securelevel to prevent userspace from inserting
untrusted privileged code at runtime.

The ACPI tables provided by firmware can be overwritten using the initrd. From the kernel documentation:

  If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible to
  override nearly any ACPI table provided by the BIOS with an instrumented,
  modified one.

RHEL7 has CONFIG_ACPI_INITRD_TABLE_OVERRIDE kernel config option enabled, and will load ACPI tables
appended to the initrd, even if booted with UEFI Secure Boot enabled and securelevel set.

Upstream patch:

The securelevel patchset was not accepted to an upstream kernel, see
and ,it is
maintained now by MJG: .

CVE-2016-3699 was assigned to this security flaw internally by the Red Hat.

Best regards,
Vladis Dronov | Red Hat, Inc. | Product Security Engineer

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