A flaw was discovered in the way that the KVM hypervisor handled instruction emulation for an L2 guest when nested virtualisation is enabled. Under some circumstances, an L2 guest may trick the L0 guest into accessing sensitive L1 resources that should be inaccessible to the L2 guest.
https://bugzilla.redhat.com/show_bug.cgi?id=1805135
https://git.kernel.org/linus/07721feee46b4b248402133228235318199b05ec
https://git.kernel.org/linus/35a571346a94fb93b5b3b6a599675ef3384bc75c
https://git.kernel.org/linus/e71237d3ff1abf9f3388337cfebf53b96df2020d
https://linux.oracle.com/errata/ELSA-2020-5540.html
https://linux.oracle.com/errata/ELSA-2020-5542.html
https://linux.oracle.com/errata/ELSA-2020-5543.html
https://lists.debian.org/debian-lts-announce/2020/06/msg00011.html
https://lists.debian.org/debian-lts-announce/2020/06/msg00012.html
https://lists.debian.org/debian-lts-announce/2020/06/msg00013.html
https://www.debian.org/security/2020/dsa-4667
https://www.debian.org/security/2020/dsa-4698
Source: MITRE
Published: 2020-04-08
Updated: 2020-06-10
Type: CWE-200
Base Score: 2.3
Vector: AV:A/AC:M/Au:S/C:P/I:N/A:N
Impact Score: 2.9
Exploitability Score: 4.4
Severity: LOW
Base Score: 6.8
Vector: CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
Impact Score: 4
Exploitability Score: 2.3
Severity: MEDIUM