FreeBSD : xen-kernel -- x86: Disallow L3 recursive pagetable for 32-bit PV guests (45ca25b5-ba4d-11e6-ae1b-002590263bf5)

Medium Nessus Plugin ID 95500

New! Vulnerability Priority Rating (VPR)

Tenable calculates a dynamic VPR for every vulnerability. VPR combines vulnerability information with threat intelligence and machine learning algorithms to predict which vulnerabilities are most likely to be exploited in attacks. Read more about what VPR is and how it's different from CVSS.

VPR Score: 6.5

Synopsis

The remote FreeBSD host is missing a security-related update.

Description

The Xen Project reports :

On real hardware, a 32-bit PAE guest must leave the USER and RW bit clear in L3 pagetable entries, but the pagetable walk behaves as if they were set. (The L3 entries are cached in processor registers, and don't actually form part of the pagewalk.)

When running a 32-bit PV guest on a 64-bit Xen, Xen must always OR in the USER and RW bits for L3 updates for the guest to observe architectural behaviour. This is unsafe in combination with recursive pagetables.

As there is no way to construct an L3 recursive pagetable in native 32-bit PAE mode, disallow this option in 32-bit PV guests.

A malicious 32-bit PV guest administrator can escalate their privilege to that of the host.

Solution

Update the affected package.

See Also

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=214936

https://xenbits.xen.org/xsa/advisory-185.html

http://www.nessus.org/u?1bd2ccd1

Plugin Details

Severity: Medium

ID: 95500

File Name: freebsd_pkg_45ca25b5ba4d11e6ae1b002590263bf5.nasl

Version: 3.2

Type: local

Published: 2016/12/05

Updated: 2018/11/10

Dependencies: 12634

Risk Information

Risk Factor: Medium

VPR Score: 6.5

CVSS v2.0

Base Score: 6.8

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:C/A:C

CVSS v3.0

Base Score: 8.2

Vector: CVSS:3.0/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Vulnerability Information

CPE: p-cpe:/a:freebsd:freebsd:xen-kernel, cpe:/o:freebsd:freebsd

Required KB Items: Host/local_checks_enabled, Host/FreeBSD/release, Host/FreeBSD/pkg_info

Patch Publication Date: 2016/12/04

Vulnerability Publication Date: 2016/09/08

Reference Information

CVE: CVE-2016-7092