FreeBSD : xen-kernel -- x86 CMPXCHG8B emulation fails to ignore operand size override (80a897a2-c1a6-11e6-ae1b-002590263bf5)

Low Nessus Plugin ID 95787


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


The Xen Project reports :

The x86 instruction CMPXCHG8B is supposed to ignore legacy operand size overrides; it only honors the REX.W override (making it CMPXCHG16B). So, the operand size is always 8 or 16. When support for CMPXCHG16B emulation was added to the instruction emulator, this restriction on the set of possible operand sizes was relied on in some parts of the emulation; but a wrong, fully general, operand size value was used for other parts of the emulation. As a result, if a guest uses a supposedly-ignored operand size prefix, a small amount of hypervisor stack data is leaked to the guests: a 96 bit leak to guests running in 64-bit mode; or, a 32 bit leak to other guests.

A malicious unprivileged guest may be able to obtain sensitive information from the host.


Update the affected package.

See Also

Plugin Details

Severity: Low

ID: 95787

File Name: freebsd_pkg_80a897a2c1a611e6ae1b002590263bf5.nasl

Version: $Revision: 3.6 $

Type: local

Published: 2016/12/14

Modified: 2017/01/31

Dependencies: 12634

Risk Information

Risk Factor: Low


Base Score: 2.1

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


Base Score: 3.3

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

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: 2016/12/14

Vulnerability Publication Date: 2016/12/13

Reference Information

CVE: CVE-2016-9932

IAVB: 2016-B-0190