xen - several

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

• CVE-2013-1917
  The SYSENTER instruction can be used by PV guests to accelerate
  system call processing. This instruction, however, leaves the EFLAGS
  register mostly unmodified. This can be used by malicious or buggy
  user space to cause the entire host to crash.
• CVE-2013-1919
  Various IRQ related access control operations may not have the
  intended effect, potentially permitting a stub domain to grant its
  client domain access to an IRQ it doesn’t have access to itself.
  This can be used by malicious or buggy stub domains kernels to mount
  a denial of service attack possibly affecting the whole system.

For the stable distribution (squeeze), these problems have been fixed in
version 4.0.1-5.9.

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

We recommend that you upgrade your xen packages.