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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD bhyve Lets Local Users on a Guest System Gain Elevated Privileges on the Host System
SecurityTracker Alert ID:  1037400
SecurityTracker URL:  http://securitytracker.com/id/1037400
CVE Reference:   CVE-2016-1889   (Links to External Site)
Date:  Dec 6 2016
Impact:   Execution of arbitrary code via local system, Root access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 10.1, 10.2, 10.3, 11.0
Description:   A vulnerability was reported in FreeBSD bhyve. A local user on the guest system can gain elevated privileges on the host system.

A local user on the guest system can supply specially crafted device descriptors to trigger an integer overflow and execute arbitrary code on the bhyve hypervisor.

Guest systems with more than 3GB are affected.

Felix Wilhelm reported this vulnerability.

Impact:   A local user on the guest system can gain root privileges on the host system.
Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-16:38.bhyve.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-16:38.bhyve.asc (Links to External Site)
Cause:   Boundary error
Underlying OS:  UNIX (FreeBSD)

Message History:   None.


 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-16:38.bhyve

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

=============================================================================
FreeBSD-SA-16:38.bhyve                                      Security Advisory
                                                          The FreeBSD Project

Topic:          bhyve(8) virtual machine escape

Category:       core
Module:         bhyve
Announced:      2016-12-06
Credits:        Felix Wilhelm
Affects:	FreeBSD 10.x, FreeBSD 11.0
Corrected:      2016-12-06 18:54:43 UTC (stable/11, 11.0-STABLE)
                2016-12-06 18:49:38 UTC (releng/11.0, 11.0-RELEASE-p4)
                2016-12-06 18:55:01 UTC (stable/10, 10.3-STABLE)
                2016-12-06 18:49:48 UTC (releng/10.3, 10.3-RELEASE-p13)
                2016-12-06 18:49:54 UTC (releng/10.2, 10.2-RELEASE-p26)
                2016-12-06 18:49:59 UTC (releng/10.1, 10.1-RELEASE-p43)
CVE Name:       CVE-2016-1889

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(8) is a hypervisor that supports running a variety of virtual
machines (guests).

II.  Problem Description

The bounds checking of accesses to guest memory greater than 4GB by
device emulations is subject to integer overflow.

III. Impact

For a bhyve virtual machine with more than 3GB of guest memory configured,
a malicious guest could craft device descriptors that could give it 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're running on.

IV.  Workaround

No workaround is available, however, systems not using bhyve(8) for
virtualization are not vulnerable. Additionally, systems using bhyve(8) with
3GB or less of configured guest memory 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(8) process for vulnerable virtual
machines should be restarted.

Perform one of the following:

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

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

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

# freebsd-update fetch
# freebsd-update install

3) 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.

[FreeBSD 11.0, FreeBSD 10.3]
# fetch https://security.FreeBSD.org/patches/SA-16:38/bhyve.patch
# fetch https://security.FreeBSD.org/patches/SA-16:38/bhyve.patch.asc
# gpg --verify bhyve.patch.asc

[FreeBSD 10.2, FreeBSD 10.1]
# fetch https://security.FreeBSD.org/patches/SA-16:38/bhyve-10.patch
# fetch https://security.FreeBSD.org/patches/SA-16:38/bhyve-10.patch.asc
# gpg --verify bhyve-10.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>.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r309648
releng/10.1/                                                      r309636
releng/10.2/                                                      r309635
releng/10.3/                                                      r309634
stable/11/                                                        r309647
releng/11.0/                                                      r309633
- -------------------------------------------------------------------------

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

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1889>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:38.bhyve.asc>
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