Xen CMPXCHG8B Emulation Information Disclosure (XSA-200)

This script is Copyright (C) 2017 Tenable Network Security, Inc.


Synopsis :

The remote Xen hypervisor installation is missing a security update.

Description :

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.

See also :

https://xenbits.xen.org/xsa/advisory-200.html
https://xenbits.xen.org/gitweb/?p=xen.git;a=summary

Solution :

Apply the appropriate patch according to the vendor advisory.

Risk factor :

Low / CVSS Base Score : 2.7
(CVSS2#AV:A/AC:L/Au:S/C:P/I:N/A:N)
CVSS Temporal Score : 2.0
(CVSS2#E:U/RL:OF/RC:C)
Public Exploit Available : false

Family: Misc.

Nessus Plugin ID: 96957 ()

Bugtraq ID: 94863

CVE ID: CVE-2016-9932

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