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Vulnerability of Xen: denial of service via Linux Event Handler Race

Synthesis of the vulnerability 

An attacker, inside a guest system, can trigger a fatal error via Linux Event Handler Race of Xen, in order to trigger a denial of service on the host system.
Impacted systems: XenServer, Fedora, Linux, SUSE Linux Enterprise Desktop, SLES.
Severity of this alert: 1/4.
Creation date: 20/10/2020.
Références of this alert: CERTFR-2020-AVI-657, CERTFR-2020-AVI-693, CERTFR-2020-AVI-741, CERTFR-2020-AVI-764, CERTFR-2020-AVI-769, CTX284874, CVE-2020-27675, FEDORA-2020-09e4d062fe, FEDORA-2020-474d747b60, FEDORA-2020-920a258c79, SUSE-SU-2020:3272-1, SUSE-SU-2020:3281-1, SUSE-SU-2020:3491-1, SUSE-SU-2020:3532-1, SUSE-SU-2020:3544-1, VIGILANCE-VUL-33629, XSA-331.

Description of the vulnerability 

An attacker, inside a guest system, can trigger a fatal error via Linux Event Handler Race of Xen, in order to trigger a denial of service on the host system.
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This cybersecurity alert impacts software or systems such as XenServer, Fedora, Linux, SUSE Linux Enterprise Desktop, SLES.

Our Vigil@nce team determined that the severity of this weakness 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 security weakness.

Solutions for this threat 

Linux kernel: version 5.9.5.
The version 5.9.5 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v5.x/

Linux kernel: version 5.4.75.
The version 5.4.75 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v5.x/

Linux kernel: version 4.19.155.
The version 4.19.155 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/

Linux kernel: version 4.14.204.
The version 4.14.204 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/

Linux kernel: patch for Xen Linux Event Handler Race.
A patch is available:
  http://xenbits.xen.org/xsa/xsa331-linux.patch

Citrix Hypervisor, XenServer: patch.
A patch is available:
  Citrix Hypervisor 8.2 LTSR: https://support.citrix.com/article/CTX285310 + https://support.citrix.com/article/CTX285316
  Citrix Hypervisor 8.1: https://support.citrix.com/article/CTX285309 + https://support.citrix.com/article/CTX285315
  Citrix XenServer 7.1 LTSR CU2: https://support.citrix.com/article/CTX285308 + https://support.citrix.com/article/CTX285314
  Citrix XenServer 7.0: https://support.citrix.com/article/CTX285307 + https://support.citrix.com/article/CTX285312

Fedora 31-33: new kernel packages.
New packages are available:
  Fedora 31: kernel 5.8.17-100.fc31
  Fedora 32: kernel 5.8.17-200.fc32
  Fedora 33: kernel 5.8.17-300.fc33

SUSE LE 12 SP4: new kernel-default packages.
New packages are available:
  SUSE LE 12 SP4: kernel-default 4.12.14-95.65.1

SUSE LE 12 SP5: new kernel-azure packages.
New packages are available:
  SUSE LE 12 SP5: kernel-azure 4.12.14-16.34.1

SUSE LE 15: new kernel packages.
New packages are available:
  SUSE LE 15 RTM: kernel-default-livepatch 4.12.14-150.63.1, kernel-livepatch 4_12_14-150_63-default-1-1.5.1

SUSE LE 15 SP1: new kernel packages.
New packages are available:
  SUSE LE 15 SP1: kernel 4.12.14-197.67.1

SUSE LE 15 SP2: new kernel-azure packages (24/11/2020).
New packages are available:
  SUSE LE 15 SP2: kernel-azure 5.3.18-18.24.1
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