xen - security update

Multiple vulnerabilities have been discovered in the Xen hypervisor. The
Common Vulnerabilities and Exposures project identifies the following
problems:

• CVE-2015-8338
  Julien Grall discovered that Xen on ARM was susceptible to denial
  of service via long running memory operations.
• CVE-2016-4480
  Jan Beulich discovered that incorrect page table handling could
  result in privilege escalation inside a Xen guest instance.
• CVE-2016-4962
  Wei Liu discovered multiple cases of missing input sanitising in
  libxl which could result in denial of service.
• CVE-2016-5242
  Aaron Cornelius discovered that incorrect resource handling on
  ARM systems could result in denial of service.
• CVE-2016-6258
  Jeremie Boutoille discovered that incorrect pagetable handling in
  PV instances could result in guest to host privilege escalation.

For the stable distribution (jessie), these problems have been fixed in
version 4.4.1-9+deb8u6.

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

We recommend that you upgrade your xen packages.