xen - denial of service

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

• CVE-2012-3494:

It was discovered that set_debugreg allows writes to reserved bits
of the DR7 debug control register on amd64 (x86-64) paravirtualised
guests, allowing a guest to crash the host.

• CVE-2012-3496:

Matthew Daley discovered that XENMEM_populate_physmap, when called
with the MEMF_populate_on_demand flag set, a BUG (detection routine)
can be triggered if a translating paging mode is not being used,
allowing a guest to crash the host.

For the stable distribution (squeeze), these problems have been fixed in
version 4.0.1-5.4.

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

For the unstable distribution (sid), these problems have been fixed in
version 4.1.3-2.

We recommend that you upgrade your xen packages.