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FreeBSD Errata Notice FreeBSD-EN-20:06.ipv6

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FreeBSD-EN-20:06.ipv6                                           Errata Notice
                                                          The FreeBSD Project

Topic:          Incorrect checksum calculations with IPv6 extension headers

Category:       core
Module:         netinet6
Announced:      2020-03-19
Credits:        Francis Dupont <>
Affects:        All supported versions of FreeBSD.
Corrected:      2020-03-02 22:54:32 UTC (stable/12, 12.1-STABLE)
                2020-03-19 16:43:37 UTC (releng/12.1, 12.1-RELEASE-p3)
                2020-03-03 08:24:09 UTC (stable/11, 11.3-STABLE)
                2020-03-19 16:43:37 UTC (releng/11.3, 11.3-RELEASE-p7)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit

I.   Background

Upper layer transport protocols, e.g., TCP, UDP, or SCTP, include
checksums in their headers.   IPv6 is a network protocol, which can
add extension headers between its own header and that of the upper
layer protocol.

II.  Problem Description

Pseudo header checksum calculations can be delayed until the IPv6
output routine or offloaded to the NIC.  In case IPv6 extension
headers are present, FreeBSD currently never offloads to the NIC.
When passing the data to the functions doing the delayed checksum
calculations, the contents of the extension headers were erroneously
included as part of the checksum.

III. Impact

Upper layer transport protocol checksums may be wrong for IPv6 packets,
such as IPv6 fragments, or IPv6 packets with a Destination Options or
Hop-by-Hop Options extension header.

IV.  Workaround

No workaround is available.  Packets sent over IPv4 or IPv6 without
any extension headers are unaffected.

V.   Solution

Upgrade your 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 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 errata update"

2) To update your 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 11.3]
# fetch
# fetch
# gpg --verify ipv6.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:> and reboot the

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r358557
releng/12.1/                                                      r359137
stable/11/                                                        r358566
releng/11.3/                                                      r359137
- -------------------------------------------------------------------------

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://

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


VII. References


The latest revision of this advisory is available at

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