xen - security update

Multiple security issues have been found in the Xen virtualisation
solution:

• CVE-2015-3209
  Matt Tait discovered a flaw in the way QEMU’s AMD PCnet Ethernet
  emulation handles multi-TMD packets with a length above 4096 bytes.
  A privileged guest user in a guest with an AMD PCNet ethernet card
  enabled can potentially use this flaw to execute arbitrary code on
  the host with the privileges of the hosting QEMU process.
• CVE-2015-4103
  Jan Beulich discovered that the QEMU Xen code does not properly
  restrict write access to the host MSI message data field, allowing
  a malicious guest to cause a denial of service.
• CVE-2015-4104
  Jan Beulich discovered that the QEMU Xen code does not properly
  restrict access to PCI MSI mask bits, allowing a malicious guest to
  cause a denial of service.
• CVE-2015-4105
  Jan Beulich reported that the QEMU Xen code enables logging for PCI
  MSI-X pass-through error messages, allowing a malicious guest to
  cause a denial of service.
• CVE-2015-4106
  Jan Beulich discovered that the QEMU Xen code does not properly restrict
  write access to the PCI config space for certain PCI pass-through devices,
  allowing a malicious guest to cause a denial of service, obtain sensitive
  information or potentially execute arbitrary code.
• CVE-2015-4163
  Jan Beulich discovered that a missing version check in the
  GNTTABOP_swap_grant_ref hypercall handler may result in denial of service.
  This only applies to Debian stable/jessie.
• CVE-2015-4164
  Andrew Cooper discovered a vulnerability in the iret hypercall handler,
  which may result in denial of service.

For the oldstable distribution (wheezy), these problems have been fixed
in version 4.1.4-3+deb7u8.

For the stable distribution (jessie), these problems have been fixed in
version 4.4.1-9+deb8u1. CVE-2015-3209, CVE-2015-4103, CVE-2015-4104,
CVE-2015-4105 and CVE-2015-4106 don’t affect the Xen package in stable
jessie, it uses the standard qemu package and has already been fixed in
DSA-3284-1.

For the unstable distribution (sid), these problems will be fixed soon.

We recommend that you upgrade your xen packages.