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FreeBSD-SA-20:21.usb_net Security Advisory
The FreeBSD Project

Topic: Potential memory corruption in USB network device drivers

Category: core
Module: kernel
Announced: 2020-08-05
Credits: Ilja van Sprundel, IOActive
Affects: All supported versions of FreeBSD.
Corrected: 2020-06-14 05:25:06 UTC (stable/12, 12.1-STABLE)
2020-08-05 17:11:18 UTC (releng/12.1, 12.1-RELEASE-p8)
2020-06-14 05:27:37 UTC (stable/11, 11.4-STABLE)
2020-08-05 17:11:18 UTC (releng/11.4, 11.4-RELEASE-p2)
2020-08-05 17:11:18 UTC (releng/11.3, 11.3-RELEASE-p12)
CVE Name: CVE-2020-7459

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

FreeBSD includes a number of USB Ethernet network interface device drivers,
including:

– smsc(4), supporting SMSC (now Microchip) devices
– muge(4), supporting Microchip devices
– cdceem(4), supporting USB Communication Device Class compatible devices

II. Problem Description

A missing length validation code common to these three drivers means that a
malicious USB device could write beyond the end of an allocated network
packet buffer.

III. Impact

An attacker with physical access to a USB port and the ability to bring a
network interface up may be able to use a specially crafted USB device to
gain kernel or user-space code execution.

IV. Workaround

No workaround is available. Systems with no active (i.e., UP) interface
supported by any of the smsc(4), muge(4), and cdceem(4) drivers are not
vulnerable.

Exploitation likely requires malicious USB hardware that emulates hardware
supported by one of these device drivers.

V. Solution

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

Perform one of the following:

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

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min “Rebooting for a security update”

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 12.x]
# fetch https://security.FreeBSD.org/patches/SA-20:21/usb_net.12.patch
# fetch https://security.FreeBSD.org/patches/SA-20:21/usb_net.12.patch.asc
# gpg –verify usb_net.12.patch.asc

[FreeBSD 11.x]
# fetch https://security.FreeBSD.org/patches/SA-20:21/usb_net.11.patch
# fetch https://security.FreeBSD.org/patches/SA-20:21/usb_net.11.patch.asc
# gpg –verify usb_net.11.patch.asc

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

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

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI. Correction details

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

Branch/path Revision
– ————————————————————————-
stable/12/ r362166
releng/12.1/ r363921
stable/11/ r362167
releng/11.4/ r363921
releng/11.3/ r363921
– ————————————————————————-

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-2020-7459>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:21.usb_net.asc>
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