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============================================================================= FreeBSD-SA-21:13.bhyve Security Advisory The FreeBSD Project
Topic: Missing error handling in bhyve(8) device models
Category: core Module: bhyve Announced: 2021-08-24 Credits: Agustin Gianni (GitHub Security Lab) Affects: All supported versions of FreeBSD. Corrected: 2021-08-24 18:29:48 UTC (stable/13, 13.0-STABLE) 2021-08-24 17:33:35 UTC (releng/13.0, 13.0-RELEASE-p4) 2021-08-24 18:33:04 UTC (stable/12, 12.2-STABLE) 2021-08-24 18:32:13 UTC (releng/12.2, 12.2-RELEASE-p10) 2021-08-24 18:33:02 UTC (stable/11, 11.4-STABLE) 2021-08-24 18:31:27 UTC (releng/11.4, 11.4-RELEASE-p13) CVE Name: CVE-2021-29631
For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit
bhyve(8) is a hypervisor that supports running a variety of guest operating systems in virtual machines. It implements a number of device models using the VirtIO interface to exchange data between the guest and the host.
II. Problem Description
Certain VirtIO-based device models failed to handle errors when fetching I/O descriptors. Such errors could be triggered by a malicious guest. As a result, the device model code could be tricked into operating on uninitialized I/O vectors, leading to memory corruption.
A malicious guest may be able to crash the bhyve process. It may be possible to exploit the memory corruption bugs to achieve arbitrary code execution in the bhyve process.
No workaround is available. Virtual machines are unaffected unless they use one or more of the following device models:
* virtio-console * virtio-rnd * virtio-scsi (available starting in FreeBSD 12.0) * virtio-9p (available starting in FreeBSD 13.0)
Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date.
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, i386, or (on FreeBSD 13 and later) arm64 platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch # freebsd-update install
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.
[FreeBSD 13.0] # fetch security.FreeBSD.org/patches/SA-21:13/bhyve.13.patch # fetch security.FreeBSD.org/patches/SA-21:13/bhyve.13.patch.asc # gpg –verify bhyve.13.patch.asc
[FreeBSD 12.2] # fetch security.FreeBSD.org/patches/SA-21:13/bhyve.12.patch # fetch security.FreeBSD.org/patches/SA-21:13/bhyve.12.patch.asc # gpg –verify bhyve.12.patch.asc
[FreeBSD 11.4] # fetch security.FreeBSD.org/patches/SA-21:13/bhyve.11.patch # fetch security.FreeBSD.org/patches/SA-21:13/bhyve.11.patch.asc # gpg –verify bhyve.11.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src # patch < /path/to/patch c) Recompile the operating system using buildworld and installworld as described in
VI. Correction details
This issue is corrected by the corresponding Git commit hash or Subversion revision number in the following stable and release branches:
Branch/path Hash Revision – ————————————————————————- stable/13/ 20f96f215562 stable/13-n246941 releng/13.0/ ec08bc89d4b3 releng/13.0-n244756 stable/12/ r370400 releng/12.2/ r370393 stable/11/ r370399 releng/11.4/ r370386 – ————————————————————————-
For FreeBSD 13 and later:
Run the following command to see which files were modified by a particular commit:
# git show –stat
Or visit the following URL, replacing NNNNNN with the hash:
To determine the commit count in a working tree (for comparison against nNNNNNN in the table above), run:
# git rev-list –count –first-parent HEAD
For FreeBSD 12 and earlier:
Run the following command to see which files were modified by a particular revision, replacing NNNNNN with the revision number:
# svn diff -cNNNNNN –summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
The latest revision of this advisory is available at
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