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FreeBSD-SA-16:32.bhyve Security Advisory
The FreeBSD Project

Topic: bhyve – privilege escalation vulnerability

Category: core
Module: bhyve
Announced: 2016-10-25
Credits: Ilja van Sprundel, IOActive
Affects: FreeBSD 11.0 amd64
Corrected: 2016-10-25 17:15:32 UTC (stable/11, 11.0-STABLE)
2016-10-25 17:11:20 UTC (releng/11.0, 11.0-RELEASE-p2)

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I. Background

bhyve is a BSD licensed hypervisor that supports running a variety of
virtual machines (guests).

II. Problem Description

An unchecked array reference in the VGA device emulation code could
potentially allow guests access to the heap of the bhyve process.
Since the bhyve process is running as root, this may allow guests to
obtain full control of the hosts they are running on.

III. Impact

For bhyve virtual machines with the “fbuf” framebuffer device
configured, if exploited, a malicious guest could obtain full access
to not just the host system, but to other virtual machines running on
the system.

IV. Workaround

No workaround is available, however systems not using bhyve for
virtualization are not vulnerable. Additionally systems using bhyve
but without the “fbuf” framebuffer device configured are not
vulnerable.

V. Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

No reboot is needed. Rather the bhyve process for vulnerable virtual
machines should be restarted.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64 platforms
can be updated via the freebsd-update(8) utility.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-16:32/bhyve.patch
# fetch https://security.FreeBSD.org/patches/SA-16:32/bhyve.patch.asc
# gpg –verify bhyve.patch.asc

b) Apply the patch. Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

Restart the bhyve process(es).

VI. Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path Revision
– ————————————————————————-
stable/11/ r307939
releng/11.0/ r307935
– ————————————————————————-

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN –summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:32.bhyve.asc>
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