Red Hat, Inc. (AV:L/AC:H/Au:N/C:C/I:C/A:C)

It was found that the Linux kernel KVM subsystem's sysenter instruction emulation was not sufficient. An unprivileged guest user could use this flaw to escalate their privileges by tricking the hypervisor to emulate a SYSENTER instruction in 16-bit mode, if the guest OS did not initialize the SYSENTER model-specific registers (MSRs). Note: Certified guest operating systems for Red Hat Enterprise Linux with KVM do initialize the SYSENTER MSRs and are thus not vulnerable to this issue when running on a KVM hypervisor.

The em_sysenter function in arch/x86/kvm/emulate.c in the Linux kernel before 3.18.5, when the guest OS lacks SYSENTER MSR initialization, allows guest OS users to gain guest OS privileges or cause a denial of service (guest OS crash) by triggering use of a 16-bit code segment for emulation of a SYSENTER instruction.

https://access.redhat.com/errata/RHSA-2015:1272 [No Types Assigned]

https://access.redhat.com/errata/RHSA-2015:2152 [No Types Assigned]

https://access.redhat.com/security/cve/CVE-2015-0239 [No Types Assigned]