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)
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