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CVE-2020-25597

Published: 23 September 2020

An issue was discovered in Xen through 4.14.x. There is mishandling of the constraint that once-valid event channels may not turn invalid. Logic in the handling of event channel operations in Xen assumes that an event channel, once valid, will not become invalid over the life time of a guest. However, operations like the resetting of all event channels may involve decreasing one of the bounds checked when determining validity. This may lead to bug checks triggering, crashing the host. An unprivileged guest may be able to crash Xen, leading to a Denial of Service (DoS) for the entire system. All Xen versions from 4.4 onwards are vulnerable. Xen versions 4.3 and earlier are not vulnerable. Only systems with untrusted guests permitted to create more than the default number of event channels are vulnerable. This number depends on the architecture and type of guest. For 32-bit x86 PV guests, this is 1023; for 64-bit x86 PV guests, and for all ARM guests, this number is 4095. Systems where untrusted guests are limited to fewer than this number are not vulnerable. Note that xl and libxl limit max_event_channels to 1023 by default, so systems using exclusively xl, libvirt+libxl, or their own toolstack based on libxl, and not explicitly setting max_event_channels, are not vulnerable.

Notes

AuthorNote
mdeslaur
hypervisor packages are in universe. For
issues in the hypervisor, add appropriate
tags to each section, ex:
Tags_xen: universe-binary

Priority

Medium

Cvss 3 Severity Score

6.5

Score breakdown

Status

Package Release Status
xen
Launchpad, Ubuntu, Debian
hirsute Ignored
(end of life)
impish Ignored
(end of life)
focal
Released (4.11.3+24-g14b62ab3e5-1ubuntu2.3)
bionic Needed

jammy Not vulnerable
(4.14.0+80-gd101b417b7-1)
xenial Needed

kinetic Not vulnerable
(4.14.0+80-gd101b417b7-1)
groovy Ignored
(end of life)
lunar Not vulnerable
(4.14.0+80-gd101b417b7-1)
trusty Does not exist

upstream Needs triage

mantic Not vulnerable
(4.14.0+80-gd101b417b7-1)
Binaries built from this source package are in Universe and so are supported by the community.

Severity score breakdown

Parameter Value
Base score 6.5
Attack vector Local
Attack complexity Low
Privileges required Low
User interaction None
Scope Changed
Confidentiality None
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H