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Advisory

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	     Xen Security Advisory CVE-2013-0154 / XSA-37

     Hypervisor crash due to incorrect ASSERT (debug build only)

ISSUE DESCRIPTION
=================

A change to an internal interface within the hypervisor invalidated an
ASSERT in a caller of that API. This code path is exposed to PV guests
via a hypercall allowing administrators of PV guests to crash the
hypervisor if it is built with debugging enabled.

IMPACT
======

Malicious administrators of PV guests running on hypervisors built
with the non-default debug=y option can crash the host.

VULNERABLE SYSTEMS
==================

Systems running Xen 4.2 and unstable are vulnerable to this issue. Xen
4.1 and earlier are not vulnerable.

Only systems built with debugging enabled are vulnerable. Debugging is
not enabled by default.

Systems running PV guests or HVM guests using stubdomains are
vulnerable. Guests which run only HVM guests without stubdomains are
not vulnerable.

MITIGATION
==========

Building the hypervisor without debugging enabled will completely
avoid this issue. Note that debugging is not enabled by default.

Avoiding running PV guests with untrusted administrators will also
avoid this issue

NOTE REGARDING LACK OF EMBARGO
==============================

This issue was disclosed publicly on xen-devel; the person reporting
it did not appreciate that it was a security issue.  Under the
circumstances the Xen.org security team do not consider that this
advisory should be embargoed.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

xsa37-4.2.patch             Xen 4.2.x
xsa37-unstable.patch        xen-unstable

$ sha256sum xsa37*.patch
beb9406e2d2de7a9768034af443b2eb30f69cd6e4688ceb63305595d2221194d  xsa37-4.2.patch
161f41f95bd679cdb19e37df4da6a75386af4689118377ec501a9e3d4f66c873  xsa37-unstable.patch
$
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