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Vulnerability of RHEL: disabling securelevel with UEFI Secure Boot

Synthesis of the vulnerability 

After some operations with UEFI Secure Boot, a local attacker can thus use kexec_load to load an unsigned kernel.
Impacted systems: RHEL, Ubuntu.
Severity of this alert: 1/4.
Creation date: 15/10/2015.
Références of this alert: CERTFR-2015-AVI-498, CERTFR-2017-AVI-275, CVE-2015-7837, RHSA-2015:2152-02, RHSA-2015:2411-01, USN-3405-1, USN-3405-2, VIGILANCE-VUL-18113.

Description of the vulnerability 

The Linux kernel can be booted with UEFI Secure Boot. In this case, securelevel is enabled.

However, if kexec is called to load the kernel, securelevel is disabled on next reboot.

After some operations with UEFI Secure Boot, a local attacker can thus use kexec_load to load an unsigned kernel.
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This threat impacts software or systems such as RHEL, Ubuntu.

Our Vigil@nce team determined that the severity of this computer threat is low.

The trust level is of type confirmed by the editor, with an origin of user shell.

An attacker with a expert ability can exploit this cybersecurity bulletin.

Solutions for this threat 

RHEL: patch for securelevel.
A patch is available:
  https://bugzilla.redhat.com/show_bug.cgi?id=1243998#c3

RHEL 7: new kernel packages (20/11/2015).
New packages are available:
  RHEL 7: kernel 3.10.0-327.el7

RHEL 7: new kernel-rt packages.
New packages are available:
  RHEL 7: kernel-rt 3.10.0-327.rt56.204.el7

Ubuntu: new linux-image-4.4.0 packages.
New packages are available:
  Ubuntu 14.04 LTS: linux-image-generic-lts-xenial 4.4.0.93.77
  Ubuntu 16.04 LTS: linux-image-generic 4.4.0.93.98
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