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AUSCERT External Security Bulletin Redistribution
ESB-2020.2679
USN-4432-2: GRUB2 regression
6 August 2020
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AusCERT Security Bulletin Summary
---------------------------------
Product: GRUB2
Publisher: Ubuntu
Operating System: Ubuntu
Impact/Access: Root Compromise -- Existing Account
Execute Arbitrary Code/Commands -- Existing Account
Increased Privileges -- Existing Account
Modify Arbitrary Files -- Existing Account
Denial of Service -- Existing Account
Resolution: Patch/Upgrade
CVE Names: CVE-2020-15707 CVE-2020-15706 CVE-2020-15705
CVE-2020-14311 CVE-2020-14310 CVE-2020-14309
CVE-2020-14308 CVE-2020-10713
Reference: ASB-2020.0136
ASB-2020.0135
ESB-2020.2647
ESB-2020.2617
ESB-2020.2590
Original Bulletin:
https://usn.ubuntu.com/4432-2/
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USN-4432-2: GRUB2 regression
04 August 2020
USN-4432-1 introduced a regression in the GRUB2 bootloader.
Releases
o Ubuntu 20.04 LTS
o Ubuntu 18.04 LTS
o Ubuntu 16.04 LTS
o Ubuntu 14.04 ESM
Packages
o grub2 - GRand Unified Bootloader
o grub2-signed - GRand Unified Bootloader
Details
USN-4432-1 fixed vulnerabilities in GRUB2 affecting Secure Boot
environments. Unfortunately, the update introduced regressions for
some BIOS systems (either pre-UEFI or UEFI configured in Legacy mode),
preventing them from successfully booting. This update addresses
the issue.
Users with BIOS systems that installed GRUB2 versions from USN-4432-1
should verify that their GRUB2 installation has a correct understanding
of their boot device location and installed the boot loader correctly.
We apologize for the inconvenience.
Original advisory details:
Jesse Michael and Mickey Shkatov discovered that the configuration parser
in GRUB2 did not properly exit when errors were discovered, resulting in
heap-based buffer overflows. A local attacker could use this to execute
arbitrary code and bypass UEFI Secure Boot restrictions. (CVE-2020-10713)
Chris Coulson discovered that the GRUB2 function handling code did not
properly handle a function being redefined, leading to a use-after-free
vulnerability. A local attacker could use this to execute arbitrary code
and bypass UEFI Secure Boot restrictions. (CVE-2020-15706)
Chris Coulson discovered that multiple integer overflows existed in GRUB2
when handling certain filesystems or font files, leading to heap-based
buffer overflows. A local attacker could use these to execute arbitrary
code and bypass UEFI Secure Boot restrictions. (CVE-2020-14309,
CVE-2020-14310, CVE-2020-14311)
It was discovered that the memory allocator for GRUB2 did not validate
allocation size, resulting in multiple integer overflows and heap-based
buffer overflows when handling certain filesystems, PNG images or disk
metadata. A local attacker could use this to execute arbitrary code and
bypass UEFI Secure Boot restrictions. (CVE-2020-14308)
Mathieu Trudel-Lapierre discovered that in certain situations, GRUB2
failed to validate kernel signatures. A local attacker could use this
to bypass Secure Boot restrictions. (CVE-2020-15705)
Colin Watson and Chris Coulson discovered that an integer overflow
existed in GRUB2 when handling the initrd command, leading to a heap-based
buffer overflow. A local attacker could use this to execute arbitrary code
and bypass UEFI Secure Boot restrictions. (CVE-2020-15707)
Update instructions
The problem can be corrected by updating your system to the following package
versions:
Ubuntu 20.04
o grub-efi-amd64-bin - 2.04-1ubuntu26.2
o grub-efi-amd64-signed - 1.142.4+2.04-1ubuntu26.2
o grub-efi-arm-bin - 2.04-1ubuntu26.2
o grub-efi-arm64-bin - 2.04-1ubuntu26.2
o grub-efi-arm64-signed - 1.142.4+2.04-1ubuntu26.2
o grub-efi-ia32-bin - 2.04-1ubuntu26.2
Ubuntu 18.04
o grub-efi-amd64-bin - 2.02-2ubuntu8.17
o grub-efi-amd64-signed - 1.93.19+2.02-2ubuntu8.17
o grub-efi-arm-bin - 2.02-2ubuntu8.17
o grub-efi-arm64-bin - 2.02-2ubuntu8.17
o grub-efi-arm64-signed - 1.93.19+2.02-2ubuntu8.17
o grub-efi-ia32-bin - 2.02-2ubuntu8.17
o grub-efi-ia64-bin - 2.02-2ubuntu8.17
Ubuntu 16.04
o grub-efi-amd64-bin - 2.02~beta2-36ubuntu3.27
o grub-efi-amd64-signed - 1.66.27+2.02~beta2-36ubuntu3.27
o grub-efi-arm-bin - 2.02~beta2-36ubuntu3.27
o grub-efi-arm64-bin - 2.02~beta2-36ubuntu3.27
o grub-efi-arm64-signed - 1.66.27+2.02~beta2-36ubuntu3.27
o grub-efi-ia32-bin - 2.02~beta2-36ubuntu3.27
o grub-efi-ia64-bin - 2.02~beta2-36ubuntu3.27
Ubuntu 14.04
o grub-efi-amd64-bin - 2.02~beta2-9ubuntu1.21
o grub-efi-amd64-signed - 1.34.20+2.02~beta2-9ubuntu1.21
o grub-efi-arm-bin - 2.02~beta2-9ubuntu1.21
o grub-efi-arm64-bin - 2.02~beta2-9ubuntu1.21
o grub-efi-ia32-bin - 2.02~beta2-9ubuntu1.21
o grub-efi-ia64-bin - 2.02~beta2-9ubuntu1.21
Fully mitigating these vulnerabilities requires both an updated
GRUB2 boot loader and the application of a UEFI Revocation
List (dbx) to system firmware. Ubuntu will provide a packaged
dbx update at a later time, though system adminstrators may
choose to apply a third party dbx update before then. For more
details on mitigation steps and the risks entailed (especially for
dual/multi-boot scenarios), please see the Knowledge Base article at
https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/GRUB2SecureBootBypass
References
o https://launchpad.net/bugs/1889556
o https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/GRUB2SecureBootBypass
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The University of Queensland
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