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FreeBSD-SA-20:27.ure                                        Security Advisory
                                                          The FreeBSD Project

Topic:          ure device driver susceptible to packet-in-packet attack

Category:       core
Module:         ure
Announced:      2020-09-15
Credits:        John-Mark Gurney
Affects:        All supported versions of FreeBSD.
Corrected:      2020-09-14 19:39:43 UTC (stable/12, 12.2-STABLE)
                2020-09-15 21:42:05 UTC (releng/12.2, 12.2-BETA1-p1)
                2020-09-15 21:42:05 UTC (releng/12.1, 12.1-RELEASE-p10)
                2020-09-15 00:22:30 UTC (stable/11, 11.4-STABLE)
                2020-09-15 21:42:05 UTC (releng/11.4, 11.4-RELEASE-p4)
                2020-09-15 21:42:05 UTC (releng/11.3, 11.3-RELEASE-p14)
CVE Name:       CVE-2020-7464

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

The ure(4) driver provides support for USB Ethernet adapters based on the
Realtek RTL8152 and RTL8153 USB Ethernet controllers.

II.  Problem Description

A programming error in the ure(4) device driver caused some Realtek USB
Ethernet interfaces to incorrectly report packets with more than 2048 bytes
in a single USB transfer as having a length of only 2048 bytes.

An adversary can exploit this to cause the driver to misinterpret part of the
payload of a large packet as a separate packet, and thereby inject packets
across security boundaries such as VLANs.

III. Impact

An attacker that can send large frames (larger than 2048 bytes in size) to be
received by the host (be it VLAN, or non-VLAN tagged packet), can inject
arbitrary packets to be received and processed by the host.  This includes
spoofing packets from other hosts, or injecting packets to other VLANs than
the host is on.

IV.  Workaround

No workaround is available.  However, an attacker needs to be able to inject
large frames.  If a switch can prevent large frames (>2048 bytes) from being
received, or connecting the machine to a switch that does not forward large
frames will mitigate this attack.

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 12.1, FreeBSD 12.2]
# fetch https://security.FreeBSD.org/patches/SA-20:27/ure.12.patch
# fetch https://security.FreeBSD.org/patches/SA-20:27/ure.12.patch.asc
# gpg --verify ure.12.patch.asc

[FreeBSD 11.3, FreeBSD 11.4]
# fetch https://security.FreeBSD.org/patches/SA-20:27/ure.11.patch
# fetch https://security.FreeBSD.org/patches/SA-20:27/ure.11.patch.asc
# gpg --verify ure.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/                                                        r365730
releng/12.2/                                                      r365778
releng/12.1/                                                      r365778
stable/11/                                                        r365738
releng/11.4/                                                      r365778
releng/11.3/                                                      r365778
- -------------------------------------------------------------------------

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-2020-7464>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:27.ure.asc>
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