CVE-2021-28711

Published: 5 January 2022

Rogue backends can cause DoS of guests via high frequency events T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Xen offers the ability to run PV backends in regular unprivileged guests, typically referred to as "driver domains". Running PV backends in driver domains has one primary security advantage: if a driver domain gets compromised, it doesn't have the privileges to take over the system. However, a malicious driver domain could try to attack other guests via sending events at a high frequency leading to a Denial of Service in the guest due to trying to service interrupts for elongated amounts of time. There are three affected backends: * blkfront patch 1, CVE-2021-28711 * netfront patch 2, CVE-2021-28712 * hvc_xen (console) patch 3, CVE-2021-28713

From the Ubuntu Security Team

Jürgen Groß discovered that the Xen subsystem within the Linux kernel did not adequately limit the number of events driver domains (unprivileged PV backends) could send to other guest VMs. An attacker in a driver domain could use this to cause a denial of service in other guest VMs.

Notes

linux-aws in 4.4 kernels (trusty and xenial) won't include
fixes for this CVE as these kernels may have xen/blkfront specific changes
and the backport is too risky.

Status