arch/x86/kvm/svm/nested.c in the Linux kernel before 5.11.12 has a use-after-free in which an AMD KVM guest can bypass access control on host OS MSRs when there are nested guests, aka CID-a58d9166a756. This occurs because of a TOCTOU race condition associated with a VMCB12 double fetch in nested_svm_vmrun.
Exploitability
AV:LAC:HPR:NUI:NScope
S:UImpact
C:HI:HA:H7.4/CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H