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Vulnerability of Xen: information disclosure via x86 FPU/XMM

Synthesis of the vulnerability 

An attacker, located in a guest system, can read a memory fragment of x86 FPU/XMM of Xen, in order to obtain sensitive information.
Vulnerable systems: XenServer, Debian, Fedora, openSUSE, openSUSE Leap, SUSE Linux Enterprise Desktop, SLES, Xen.
Severity of this threat: 1/4.
Creation date: 17/12/2015.
Références of this weakness: CERTFR-2015-AVI-551, CERTFR-2015-AVI-556, CTX203879, CVE-2015-8555, DLA-479-1, DSA-3519-1, FEDORA-2015-c44bd3e0fa, FEDORA-2015-d8253e2b1d, openSUSE-SU-2016:0123-1, openSUSE-SU-2016:0124-1, openSUSE-SU-2016:0126-1, SUSE-SU-2016:0658-1, SUSE-SU-2016:0873-1, SUSE-SU-2016:0955-1, SUSE-SU-2016:1154-1, SUSE-SU-2016:1318-1, SUSE-SU-2016:1745-1, VIGILANCE-VUL-18554, XSA-165.

Description of the vulnerability 

The XSAVE and XRSTOR instructions are used to save and restore the processor state.

However, when Xen is on a x86 processor without XSAVE/XRSTOR, a guest system can read the FPU stack and previous XMM registers.

An attacker, located in a guest system, can therefore read a memory fragment of x86 FPU/XMM of Xen, in order to obtain sensitive information.
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This security threat impacts software or systems such as XenServer, Debian, Fedora, openSUSE, openSUSE Leap, SUSE Linux Enterprise Desktop, SLES, Xen.

Our Vigil@nce team determined that the severity of this computer weakness note is low.

The trust level is of type confirmed by the editor, with an origin of user shell.

An attacker with a expert ability can exploit this computer threat alert.

Solutions for this threat 

Xen: patch for x86 FPU/XMM.
A patch is available:
  http://xenbits.xen.org/xsa/advisory-165.html

Citrix XenServer: patch.
A patch is indicated in information sources.

Debian 7: new xen packages.
New packages are available:
  Debian 7: xen 4.1.6.1-1+deb7u1

Debian: new xen packages.
New packages are available:
  Debian 8: xen 4.4.1-9+deb8u4

Fedora: new xen packages.
New packages are available:
  Fedora 22: xen 4.5.2-6.fc22
  Fedora 23: xen 4.5.2-6.fc23

openSUSE 13.1: new xen packages (15/01/2016).
New packages are available:
  openSUSE 13.1: xen 4.3.4_10-53.1

openSUSE 13.2: new xen packages (15/01/2016).
New packages are available:
  openSUSE 13.2: xen 4.4.3_08-36.1

openSUSE Leap 42.1: new xen packages (15/01/2016).
New packages are available:
  openSUSE Leap 42.1: xen 4.5.2_04-9.2

SUSE LE 10: new xen packages (07/03/2016).
New packages are available:
  SUSE LE 10 SP4: xen 3.2.3_17040_46-0.23.2

SUSE LE 11 SP2: new xen packages (27/04/2016).
New packages are available:
  SUSE LE 11 SP2: xen 4.1.6_08-26.1

SUSE LE 11 SP3: new xen packages (06/07/2016).
New packages are available:
  SUSE LE 11 SP3: xen-kmp-default 4.2.5_20_3.0.101_0.47.79-24.9, xen-libs 4.2.5_20-24.9, xen-tools-domU 4.2.5_20-24.9

SUSE LE 11 SP4: new xen packages (05/04/2016).
New packages are available:
  SUSE LE 11 SP4: xen 4.4.4_02-32.1

SUSE LE 12: new xen packages.
New packages are available:
  SUSE LE 12 RTM: xen 4.4.4_02-22.19.1

SUSE LE 12 SP1: new xen packages.
New packages are available:
  SUSE LE 12 SP1: xen 4.5.2_06-7.1
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