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FreeBSD-SA-18:05.ipsec                                      Security Advisory
                                                          The FreeBSD Project

Topic:          ipsec crash or denial of service

Category:       core
Module:         ipsec
Announced:      2018-04-04
Credits:        Maxime Villard
Affects:        All supported versions of FreeBSD.
Corrected:      2018-01-31 09:24:48 UTC (stable/11, 11.1-STABLE)
                2018-04-04 05:37:52 UTC (releng/11.1, 11.1-RELEASE-p9)
                2018-01-31 09:26:28 UTC (stable/10, 10.4-STABLE)
                2018-04-04 05:37:52 UTC (releng/10.4, 10.4-RELEASE-p8)
                2018-04-04 05:37:52 UTC (releng/10.3, 10.3-RELEASE-p29)
CVE Name:       CVE-2018-6918

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 IPsec suite of protocols provide network level security for IPv4 and IPv6
packets.  FreeBSD includes software originally developed by the KAME project
which implements the various protocols that make up IPsec.

In IPsec, the IP Authentication Header (AH) is used to provide protection
against replay attacks and connectionless integrity and data origin
authentication for IP datagrams.

II.  Problem Description

The length field of the option header does not count the size of the option
header itself.  This causes a problem when the length is zero, the count is
then incremented by zero, which causes an infinite loop.

In addition there are pointer/offset mistakes in the handling of IPv4
options.

III. Impact

A remote attacker who is able to send an arbitrary packet, could cause the
remote target machine to crash.

IV.  Workaround

No workaround is available.  Note that in FreeBSD 10 IPsec is not included
in the kernel by default, but it is in FreeBSD 11.

V.   Solution

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.

Afterward, reboot the system.

2) 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

Afterward, reboot the system.

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.

# fetch https://security.FreeBSD.org/patches/SA-18:05/ipsec.patch
# fetch https://security.FreeBSD.org/patches/SA-18:05/ipsec.patch.asc
# gpg --verify ipsec.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/10/                                                        r328621
releng/10.3/                                                      r331985
releng/10.4/                                                      r331985
stable/11/                                                        r328620
releng/11.1/                                                      r331985
- -------------------------------------------------------------------------

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-2018-6918>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:05.ipsec.asc>
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