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Vulnerability of Xen: privilege escalation via Cache Write-back Under VT-d

Synthesis of the vulnerability 

An attacker, inside a guest system, can bypass restrictions via Cache Write-back Under VT-d of Xen, in order to escalate his privileges on the host system.
Impacted software: XenServer, Debian, Fedora, openSUSE Leap, SUSE Linux Enterprise Desktop, SLES, Xen.
Severity of this computer vulnerability: 2/4.
Creation date: 07/07/2020.
Références of this announce: CERTFR-2020-AVI-414, CERTFR-2020-AVI-418, CTX277456, CVE-2020-15565, DSA-4723-1, FEDORA-2020-76cf2b0f0a, FEDORA-2020-fbc13516af, openSUSE-SU-2020:0965-1, openSUSE-SU-2020:0985-1, SUSE-SU-2020:14521-1, SUSE-SU-2020:1886-1, SUSE-SU-2020:1887-1, SUSE-SU-2020:1888-1, SUSE-SU-2020:1889-1, SUSE-SU-2020:1891-1, SUSE-SU-2020:2822-1, VIGILANCE-VUL-32740, XSA-321.

Description of the vulnerability 

An attacker, inside a guest system, can bypass restrictions via Cache Write-back Under VT-d of Xen, in order to escalate his privileges on the host system.
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This vulnerability bulletin impacts software or systems such as XenServer, Debian, Fedora, openSUSE Leap, SUSE Linux Enterprise Desktop, SLES, Xen.

Our Vigil@nce team determined that the severity of this security note is medium.

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 cybersecurity note.

Solutions for this threat 

Xen: patch for Cache Write-back Under VT-d.
A patch is available:
  http://xenbits.xen.org/xsa/xsa321/xsa321-1.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-2.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-3.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-1.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-2.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-3.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-4.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-5.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-6.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.9-7.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-1.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-2.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-3.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-4.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-5.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-6.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.10-7.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-1.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-2.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-3.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-4.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-5.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-6.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.11-7.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-1.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-2.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-3.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-4.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-5.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-6.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.12-7.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-1.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-2.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-3.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-4.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-5.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-6.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.13-7.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-4.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-5.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-6.patch
  http://xenbits.xen.org/xsa/xsa321/xsa321-7.patch

Citrix Hypervisor: patch for Xen.
A patch is available:
  Citrix Hypervisor 8.2 LTSR: CTX277444 - https://support.citrix.com/article/CTX277444
  Citrix Hypervisor 8.1: CTX277443 - https://support.citrix.com/article/CTX277443
  Citrix Hypervisor 8.0: CTX277442 - https://support.citrix.com/article/CTX277442
  Citrix XenServer 7.1 LTSR CU2: CTX277441 - https://support.citrix.com/article/CTX277441
  Citrix XenServer 7.0: CTX277440 - https://support.citrix.com/article/CTX277440

Debian 10: new xen packages.
New packages are available:
  Debian 10: xen 4.11.4+24-gddaaccbbab-1~deb10u1

Fedora 31: new xen packages.
New packages are available:
  Fedora 31: xen 4.12.3-3.fc31

Fedora 32: new xen packages.
New packages are available:
  Fedora 32: xen 4.13.1-4.fc32

openSUSE Leap 15.1: new xen packages (16/07/2020).
New packages are available:
  openSUSE Leap 15.1: xen 4.12.3_04-lp151.2.21.1

openSUSE Leap 15.2: new xen packages.
New packages are available:
  openSUSE Leap 15.2: xen 4.13.1_04-lp152.2.3.1

SUSE LE 11 SP4: new xen packages.
New packages are available:
  SUSE LE 11 SP4: xen 4.4.4_44-61.55.1

SUSE LE 12 SP2: new xen packages.
New packages are available:
  SUSE LE 12 SP2: xen 4.7.6_10-43.67.1

SUSE LE: new xen packages.
New packages are available:
  SUSE LE 12 SP3: xen 4.9.4_08-3.66.1
  SUSE LE 12 SP4: xen 4.11.4_04-2.30.1
  SUSE LE 12 SP5: xen 4.12.3_04-3.18.1
  SUSE LE 15 RTM: xen 4.10.4_12-3.35.1
  SUSE LE 15 SP1: xen 4.12.3_04-3.22.1
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