inverted code paths in x86 dirty VRAM tracking

2020-07-0712:00:00

Xen Project

xenbits.xen.org

6.5 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

4.7 Medium

CVSS2

Access Vector

LOCAL

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

COMPLETE

AV:L/AC:M/Au:N/C:N/I:N/A:C

0.0004 Low

EPSS

Percentile

13.4%

JSON

ISSUE DESCRIPTION

An inverted conditional in x86 HVM guests’ dirty video RAM tracking code allows such guests to make Xen de-reference a pointer guaranteed to point at unmapped space.

IMPACT

A malicious or buggy HVM guest may cause the hypervisor to crash, resulting in Denial of Service (DoS) affecting the entire host.

VULNERABLE SYSTEMS

Xen versions from 4.8 onwards are affected. Xen versions 4.7 and earlier are not affected.
Only x86 systems are affected. Arm systems are not affected.
Only x86 HVM guests using shadow paging can leverage the vulnerability. In addition there needs to be an entity actively monitoring a guest’s video frame buffer (typically for display purposes) in order for such a guest to be able to leverage the vulnerability. x86 PV guests as well as x86 HVM guest using hardware assisted paging (HAP) cannot leverage the vulnerability.