CVE-2016-4020: Canonical Ubuntu Linux

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

The patch_instruction function in hw/i386/kvmvapic.c in QEMU does not initialize the imm32 variable, which allows local guest OS administrators to obtain sensitive information from host stack memory by accessing the Task Priority Register (TPR).

Affected products

• Canonical Ubuntu Linux: version 12.04 only; version 14.04 only; version 15.10 only; version 16.04 only
• Debian Debian Linux: version 8.0 only
• Qemu Qemu: up to and including 2.6.2
• Red Hat Enterprise Linux Desktop: version 7.0 only
• Red Hat Enterprise Linux Eus: version 7.4 only; version 7.5 only; version 7.6 only; version 7.7 only
• Red Hat Enterprise Linux Server: version 7.0 only
• Red Hat Enterprise Linux Server Aus: version 7.4 only; version 7.6 only; version 7.7 only
• Red Hat Enterprise Linux Server Tus: version 7.6 only; version 7.7 only
• Red Hat Enterprise Linux Workstation: version 7.0 only
• Red Hat Openstack: version 6.0 only; version 7.0 only; version 8 only; version 9 only; version 10 only; version 11 only
• Red Hat Virtualization: version 4.0 only

Published 2016-05-25. Last modified 2026-06-17.