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CVE-2019-18420

Published: 31 October 2019

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via a VCPUOP_initialise hypercall. hypercall_create_continuation() is a variadic function which uses a printf-like format string to interpret its parameters. Error handling for a bad format character was done using BUG(), which crashes Xen. One path, via the VCPUOP_initialise hypercall, has a bad format character. The BUG() can be hit if VCPUOP_initialise executes for a sufficiently long period of time for a continuation to be created. Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier are not vulnerable. Only x86 PV guests can exploit the vulnerability. HVM and PVH guests, and guests on ARM systems, cannot exploit the vulnerability.

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
disco Ignored
(end of life)
eoan Ignored
(end of life)
focal Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
trusty Does not exist

upstream Needs triage

bionic Needed

impish Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
groovy Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
xenial Needed

hirsute Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
jammy Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
kinetic Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
lunar Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
mantic Not vulnerable
(4.11.3+24-g14b62ab3e5-1ubuntu1)
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 Network
Attack complexity Low
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality None
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H