The grub2 package before 2.02-0.29 in Red Hat Enterprise Linux (RHEL) 7, when used on UEFI systems, allows local users to bypass intended Secure Boot restrictions and execute non-verified code via a crafted (1) multiboot or (2) multiboot2 module in the configuration file or physically proximate attackers to bypass intended Secure Boot restrictions and execute non-verified code via the (3) boot menu.

Rebuild without multiboot* modules in the EFI image.

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

It was discovered that grub2 builds for EFI systems contained modules that were not suitable to be loaded in a Secure Boot environment. An attacker could use this flaw to circumvent the Secure Boot mechanisms and load non- verified code. Attacks could use the boot menu if no password was set, or the grub2 configuration file if the attacker has root privileges on the system. (CVE-2015-5281)

This update also fixes the following bugs :

  - In one of the earlier updates, GRUB2 was modified to     escape forward slash (/) characters in several different     places. In one of these places, the escaping was     unnecessary and prevented certain types of kernel     command-line arguments from being passed to the kernel     correctly. With this update, GRUB2 no longer escapes the     forward slash characters in the mentioned place, and the     kernel command-line arguments work as expected.

  - Previously, GRUB2 relied on a timing mechanism provided     by legacy hardware, but not by the Hyper-V Gen2     hypervisor, to calibrate its timer loop. This prevented     GRUB2 from operating correctly on Hyper-V Gen2. This     update modifies GRUB2 to use a different mechanism on     Hyper-V Gen2 to calibrate the timing. As a result,     Hyper-V Gen2 hypervisors now work as expected.

  - Prior to this update, users who manually configured     GRUB2 to use the built-in GNU Privacy Guard (GPG)     verification observed the following error on boot :

alloc magic is broken at [addr]: [value] Aborted.

Consequently, the boot failed. The GRUB2 built-in GPG verification has been modified to no longer free the same memory twice. As a result, the mentioned error no longer occurs.

  - Previously, the system sometimes did not recover after     terminating unexpectedly and failed to reboot. To fix     this problem, the GRUB2 packages now enforce file     synchronization when creating the GRUB2 configuration     file, which ensures that the required configuration     files are written to disk. As a result, the system now     reboots successfully after crashing.

  - Previously, if an unconfigured network driver instance     was selected and configured when the GRUB2 bootloader     was loaded on a different instance, GRUB2 did not     receive notifications of the Address Resolution Protocol     (ARP) replies. Consequently, GRUB2 failed with the     following error message :

error: timeout: could not resolve hardware address.

With this update, GRUB2 selects the network driver instance from which it was loaded. As a result, ARP packets are processed correctly.

In addition, this update adds the following enhancement :

  - Sorting of GRUB2 boot menu has been improved. GRUB2 now     uses the rpmdevtools package to sort available kernels     and the configuration file is being generated correctly     with the most recent kernel version listed at the top.

Updated grub2 packages that fix one security issue, several bugs, and add one enhancement are now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Low security impact. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available from the CVE link in the References section.

The grub2 packages provide version 2 of the Grand Unified Bootloader (GRUB), a highly configurable and customizable bootloader with modular architecture. The packages support a variety of kernel formats, file systems, computer architectures, and hardware devices.

It was discovered that grub2 builds for EFI systems contained modules that were not suitable to be loaded in a Secure Boot environment. An attacker could use this flaw to circumvent the Secure Boot mechanisms and load non-verified code. Attacks could use the boot menu if no password was set, or the grub2 configuration file if the attacker has root privileges on the system. (CVE-2015-5281)

This update also fixes the following bugs :

* In one of the earlier updates, GRUB2 was modified to escape forward slash (/) characters in several different places. In one of these places, the escaping was unnecessary and prevented certain types of kernel command-line arguments from being passed to the kernel correctly. With this update, GRUB2 no longer escapes the forward slash characters in the mentioned place, and the kernel command-line arguments work as expected. (BZ#1125404)

* Previously, GRUB2 relied on a timing mechanism provided by legacy hardware, but not by the Hyper-V Gen2 hypervisor, to calibrate its timer loop. This prevented GRUB2 from operating correctly on Hyper-V Gen2. This update modifies GRUB2 to use a different mechanism on Hyper-V Gen2 to calibrate the timing. As a result, Hyper-V Gen2 hypervisors now work as expected. (BZ#1150698)

* Prior to this update, users who manually configured GRUB2 to use the built-in GNU Privacy Guard (GPG) verification observed the following error on boot :

alloc magic is broken at [addr]: [value] Aborted.

Consequently, the boot failed. The GRUB2 built-in GPG verification has been modified to no longer free the same memory twice. As a result, the mentioned error no longer occurs. (BZ#1167977)

* Previously, the system sometimes did not recover after terminating unexpectedly and failed to reboot. To fix this problem, the GRUB2 packages now enforce file synchronization when creating the GRUB2 configuration file, which ensures that the required configuration files are written to disk. As a result, the system now reboots successfully after crashing. (BZ#1212114)

* Previously, if an unconfigured network driver instance was selected and configured when the GRUB2 bootloader was loaded on a different instance, GRUB2 did not receive notifications of the Address Resolution Protocol (ARP) replies. Consequently, GRUB2 failed with the following error message :

error: timeout: could not resolve hardware address.

With this update, GRUB2 selects the network driver instance from which it was loaded. As a result, ARP packets are processed correctly.
(BZ#1257475)

In addition, this update adds the following enhancement :

* Sorting of GRUB2 boot menu has been improved. GRUB2 now uses the rpmdevtools package to sort available kernels and the configuration file is being generated correctly with the most recent kernel version listed at the top. (BZ#1124074)

All grub2 users are advised to upgrade to these updated packages, which contain backported patches to correct these issues and add this enhancement.

The remote Oracle Linux 7 host has packages installed that are affected by a vulnerability as referenced in the ELSA-2015-2401 advisory.

    - Once again, rebuild for the right build target.
      Resolves: CVE-2015-5281
    - Remove multiboot and multiboot2 modules from the .efi builds; they       should never have been there.
      Resolves: CVE-2015-5281

Tenable has extracted the preceding description block directly from the Oracle Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The remote Redhat Enterprise Linux 7 host has packages installed that are affected by a vulnerability as referenced in the RHSA-2015:2401 advisory.

    The grub2 packages provide version 2 of the Grand Unified Bootloader     (GRUB), a highly configurable and customizable bootloader with modular     architecture. The packages support a variety of kernel formats, file     systems, computer architectures, and hardware devices.

    It was discovered that grub2 builds for EFI systems contained modules that     were not suitable to be loaded in a Secure Boot environment. An attacker     could use this flaw to circumvent the Secure Boot mechanisms and load     non-verified code. Attacks could use the boot menu if no password was set,     or the grub2 configuration file if the attacker has root privileges on the     system. (CVE-2015-5281)

    This update also fixes the following bugs:

    * In one of the earlier updates, GRUB2 was modified to escape forward slash     (/) characters in several different places. In one of these places, the     escaping was unnecessary and prevented certain types of kernel command-line     arguments from being passed to the kernel correctly. With this update,     GRUB2 no longer escapes the forward slash characters in the mentioned     place, and the kernel command-line arguments work as expected. (BZ#1125404)

    * Previously, GRUB2 relied on a timing mechanism provided by legacy     hardware, but not by the Hyper-V Gen2 hypervisor, to calibrate its timer     loop. This prevented GRUB2 from operating correctly on Hyper-V Gen2.
    This update modifies GRUB2 to use a different mechanism on Hyper-V Gen2 to     calibrate the timing. As a result, Hyper-V Gen2 hypervisors now work as     expected. (BZ#1150698)

    * Prior to this update, users who manually configured GRUB2 to use the     built-in GNU Privacy Guard (GPG) verification observed the following error     on boot:

        alloc magic is broken at [addr]: [value] Aborted.

    Consequently, the boot failed. The GRUB2 built-in GPG verification has been     modified to no longer free the same memory twice. As a result, the     mentioned error no longer occurs. (BZ#1167977)

    * Previously, the system sometimes did not recover after terminating     unexpectedly and failed to reboot. To fix this problem, the GRUB2 packages     now enforce file synchronization when creating the GRUB2 configuration     file, which ensures that the required configuration files are written to     disk. As a result, the system now reboots successfully after crashing.
    (BZ#1212114)

    * Previously, if an unconfigured network driver instance was selected and     configured when the GRUB2 bootloader was loaded on a different instance,     GRUB2 did not receive notifications of the Address Resolution Protocol     (ARP) replies. Consequently, GRUB2 failed with the following error message:

        error: timeout: could not resolve hardware address.

    With this update, GRUB2 selects the network driver instance from which it     was loaded. As a result, ARP packets are processed correctly. (BZ#1257475)

    In addition, this update adds the following enhancement:

    * Sorting of GRUB2 boot menu has been improved. GRUB2 now uses the     rpmdevtools package to sort available kernels and the configuration file is     being generated correctly with the most recent kernel version listed at the     top. (BZ#1124074)

    All grub2 users are advised to upgrade to these updated packages, which     contain backported patches to correct these issues and add this     enhancement.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Severity
89396	Fedora 23 : grub2-2.02-0.24.fc23 (2015-c3b4fef3af)	Nessus	Fedora Local Security Checks	low
89190	Fedora 22 : grub2-2.02-0.17.fc22 (2015-2c155d7632)	Nessus	Fedora Local Security Checks	low
87558	Scientific Linux Security Update : grub2 on SL7.x x86_64 (20151119)	Nessus	Scientific Linux Local Security Checks	low
87157	CentOS 7 : grub2 (CESA-2015:2401)	Nessus	CentOS Local Security Checks	low
87039	Oracle Linux 7 : grub2 (ELSA-2015-2401)	Nessus	Oracle Linux Local Security Checks	critical
86989	RHEL 7 : grub2 (RHSA-2015:2401)	Nessus	Red Hat Local Security Checks	critical

Detections

Analytics

CVE-2015-5281

high

Tenable Plugins

low

low

low

low

critical

critical