Xen CMPXCHG8B Emulation Information Disclosure (XSA-200)

Low Nessus Plugin ID 96957


The remote Xen hypervisor installation is missing a security update.


According to its self-reported version number, the Xen hypervisor installed on the remote host is missing a security update. It is, therefore, affected by an information disclosure vulnerability due to a flaw in the x86 instruction CMPXCHG8B when handling prefixes. This is triggered because legacy operand size overrides are not properly ignored. A guest attacker can exploit this issue to disclose potentially sensitive information from the hypervisor stack of the host system.

Please note the following items :

- Only x86 systems are affected. ARM systems are not affected.

- On Xen version 4.6 and earlier, the vulnerability is exposed to all HVM guest user processes, including unprivileged processes.

- On Xen version 4.7, the vulnerability is exposed only to HVM guest user processes granted a degree of privilege (e.g., direct hardware access) by the guest administrator, or else to all user processes when the VM has been explicitly configured with a non-default CPU vendor string (in xm/xl, this would be done with a 'cpuid=' domain config option).

Note that Nessus has not tested for this vulnerability but has instead relied only on the changeset versions based on the xen.git change log.
Nessus did not check guest hardware configurations or if patches were applied manually to the source code before a recompile and reinstall.


Apply the appropriate patch according to the vendor advisory.

See Also



Plugin Details

Severity: Low

ID: 96957

File Name: xen_server_XSA-200.nasl

Version: 1.6

Type: local

Family: Misc.

Published: 2017/02/02

Updated: 2018/08/08

Dependencies: 78089

Configuration: Enable paranoid mode

Risk Information

Risk Factor: Low

CVSS v2.0

Base Score: 2.7

Temporal Score: 2

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

Temporal Vector: CVSS2#E:U/RL:OF/RC:C

CVSS v3.0

Base Score: 4.1

Temporal Score: 3.6

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

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:xen:xen

Required KB Items: installed_sw/Xen Hypervisor, Settings/ParanoidReport

Exploit Available: false

Exploit Ease: No known exploits are available

Patch Publication Date: 2016/12/13

Vulnerability Publication Date: 2016/12/13

Reference Information

CVE: CVE-2016-9932

BID: 94863