Ubuntu Security Notice 5467-1 - It was discovered that the Linux kernel did not properly restrict access to the kernel debugger when booted in secure boot environments. A privileged attacker could use this to bypass UEFI Secure Boot restrictions. Aaron Adams discovered that the netfilter subsystem in the Linux kernel did not properly handle the removal of stateful expressions in some situations, leading to a use-after-free vulnerability. A local attacker could use this to cause a denial of service or execute arbitrary code.
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Ubuntu Security Notice 5418-1 - Ke Sun, Alyssa Milburn, Henrique Kawakami, Emma Benoit, Igor Chervatyuk, Lisa Aichele, and Thais Moreira Hamasaki discovered that the Spectre Variant 2 mitigations for AMD processors on Linux were insufficient in some situations. A local attacker could possibly use this to expose sensitive information. Demi Marie Obenour and Simon Gaiser discovered that several Xen para- virtualization device frontends did not properly restrict the access rights of device backends. An attacker could possibly use a malicious Xen backend to gain access to memory pages of a guest VM or cause a denial of service in the guest.
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