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Advisory

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              Xen Security Advisory CVE-2014-4021 / XSA-100
                             version 3

              Hypervisor heap contents leaked to guests

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

Public Release.  CVE assigned.

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

While memory pages recovered from dying guests are being cleaned to avoid
leaking sensitive information to other guests, memory pages that were in
use by the hypervisor and are eligible to be allocated to guests weren't
being properly cleaned.  Such exposure of information would happen through
memory pages freshly allocated to or by the guest.

Normally the leaked data is administrative information of limited
value to an attacker.  However, scenarios exist where guest CPU
register state and hypercall arguments might be leaked.

IMPACT
======

A malicious guest might be able to read data relating to other guests
or the hypervisor itself.

Data at rest in guest memory or storage (filesystems) is not affected.
However, it is possible for an attacker to obtain modest amounts of
in-flight and in-use data, which might contain passwords or
cryptographic keys.

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

Xen 3.2.x and later are vulnerable.
Xen 3.1.x and earlier have not been inspected.

MITIGATION
==========

No comprehensive mitigation is available.

An attacker will find it easier obtain sensitive data from a victim
guest if the attacker is able to initiate domain management operations
and lifecycle events for that guest.  This includes a situation where
the attacker can cause the victim guest to crash.

Therefore the risk from this vulnerability can be somewhat reduced by
restricting management (such as migration or resource adjustment) to
fully trusted guest or host administrators, and by eliminating any
Denial of Service vulnerabilities against potential victim guests.

CREDITS
=======

This issue was discovered by Jan Beulich.

RESOLUTION
==========

Applying the attached patch resolves this issue.

xsa100.patch        xen-unstable, Xen 4.4.x, Xen 4.3.x, Xen 4.2.x, Xen 4.1.x

Note that to avoid a regression on systems with AMD IOMMU, on 4.2.x and later
additionally commit 6b4d71d0 ("AMD IOMMU: don't free page table prematurely")
found at
http://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=6b4d71d028f445cba7426a144751fddc8bfdd67b
will be required if not already in place in the respective tree.

$ sha256sum xsa100*.patch
2cbd3a52bb8d32d00a19e2ce48e3157034b484b4a7b7282cae0d108ffb4ddca0  xsa100.patch
$
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