========================================================================= Ubuntu Security Notice USN-5091-3 October 15, 2021 linux-azure, linux-azure-5.4 regression ========================================================================= A security issue affects these releases of Ubuntu and its derivatives: - Ubuntu 20.04 LTS - Ubuntu 18.04 LTS Summary: USN-5091-1 introduced a regression in the Linux kernel for Microsoft Azure cloud systems. Software Description: - linux-azure: Linux kernel for Microsoft Azure Cloud systems - linux-azure-5.4: Linux kernel for Microsoft Azure cloud systems Details: USN-5091-1 fixed vulnerabilities in Linux 5.4-based kernels. Unfortunately, for Linux kernels intended for use within Microsoft Azure environments, that update introduced a regression that could cause the kernel to fail to boot in large Azure instance types. This update fixes the problem. We apologize for the inconvenience. Original advisory details: Ofek Kirzner, Adam Morrison, Benedict Schlueter, and Piotr Krysiuk discovered that the BPF verifier in the Linux kernel missed possible mispredicted branches due to type confusion, allowing a side-channel attack. An attacker could use this to expose sensitive information. (CVE-2021-33624) It was discovered that the tracing subsystem in the Linux kernel did not properly keep track of per-cpu ring buffer state. A privileged attacker could use this to cause a denial of service. (CVE-2021-3679) Alexey Kardashevskiy discovered that the KVM implementation for PowerPC systems in the Linux kernel did not properly validate RTAS arguments in some situations. An attacker in a guest vm could use this to cause a denial of service (host OS crash) or possibly execute arbitrary code. (CVE-2021-37576) It was discovered that the Virtio console implementation in the Linux kernel did not properly validate input lengths in some situations. A local attacker could possibly use this to cause a denial of service (system crash). (CVE-2021-38160) Michael Wakabayashi discovered that the NFSv4 client implementation in the Linux kernel did not properly order connection setup operations. An attacker controlling a remote NFS server could use this to cause a denial of service on the client. (CVE-2021-38199) It was discovered that the MAX-3421 host USB device driver in the Linux kernel did not properly handle device removal events. A physically proximate attacker could use this to cause a denial of service (system crash). (CVE-2021-38204) Update instructions: The problem can be corrected by updating your system to the following package versions: Ubuntu 20.04 LTS: linux-image-5.4.0-1061-azure 5.4.0-1061.64 linux-image-azure-lts-20.04 5.4.0.1061.59 Ubuntu 18.04 LTS: linux-image-5.4.0-1061-azure 5.4.0-1061.64~18.04.1 linux-image-azure 5.4.0.1061.41 After a standard system update you need to reboot your computer to make all the necessary changes. ATTENTION: Due to an unavoidable ABI change the kernel updates have been given a new version number, which requires you to recompile and reinstall all third party kernel modules you might have installed. Unless you manually uninstalled the standard kernel metapackages (e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual, linux-powerpc), a standard system upgrade will automatically perform this as well. References: https://ubuntu.com/security/notices/USN-5091-3 https://ubuntu.com/security/notices/USN-5091-1 https://launchpad.net/bugs/1940564 Package Information: https://launchpad.net/ubuntu/+source/linux-azure/5.4.0-1061.64 https://launchpad.net/ubuntu/+source/linux-azure-5.4/5.4.0-1061.64~18.04.1