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Advisory

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             Xen Security Advisory CVE-2014-1896 / XSA-86
                              version 3

           libvchan failure handling malicious ring indexes

UPDATES IN VERSION 3
====================

CVE assigned.

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

libvchan (a library for inter-domain communication) does not correctly
handle unusual or malicious contents in the xenstore ring.  A
malicious guest can exploit this to cause a libvchan-using facility to
read or write past the end of the ring.

IMPACT
======

libvchan-using facilities are vulnerable to denial of service and
perhaps privilege escalation.

There are no such services provided in the upstream Xen Project
codebase.

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

All versions of libvchan are vulnerable.  Only installations which use
libvchan for communication involving untrusted domains are vulnerable.

libvirt, xapi, xend, libxl and xl do not use libvchan.  If your
installation contains other Xen-related software components it is
possible that they use libvchan and might be vulnerable.

Xen versions 4.1 and earlier do not contain libvchan.

MITIGATION
==========

Disabling libvchan-based facilities could be used to mitigate the
vulnerability.

CREDITS
=======

This issue was discovered by Marek Marczykowski-Górecki of Invisible
Things Lab.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

After the patch is applied to the Xen tree and built, any software
which is statically linked against libvchan will need to be relinked
against the new libvchan.a for the fix to take effect.

xsa86.patch        Xen 4.2.x, 4.3.x, 4.4-RC series, and xen-unstable

$ sha256sum xsa86*.patch
cd2df017e42717dd2a1b6f2fdd3ad30a38d3c0fbdd9d08b5f56ee0a01cd87b51  xsa86.patch
$
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