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FreeBSD-EN-18:13.icmp                                           Errata Notice
                                                          The FreeBSD Project

Topic:          ICMP buffer underwrite

Category:       core
Module:         kernel
Announced:      2018-11-27
Affects:        All supported versions of FreeBSD.
Corrected:      2018-11-08 21:58:51 UTC (stable/11, 11.2-STABLE)
                2018-11-27 19:43:16 UTC (releng/11.2, 11.2-RELEASE-p5)
CVE Name:       CVE-2018-17156

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

ICMP messages are control messages used to send error messages and 
operational information.

II.  Problem Description

The icmp_error routine allocates either an mbuf or a cluster depending on the
size of the data to be quoted in the ICMP reply, but the calculation failed
to account for additional padding on 64-bit platforms when using a
non-default sysctl value for net.inet.icmp.quotelen.

III. Impact

For systems that set net.inet.icmp.quotelen to a non-default value, a buffer
underwrite condition occurs.

IV.  Workaround

Reset net.inet.icmp.quotelen to default value of 8 using sysctl(8):

# sysctl net.inet.icmp.quotelen=8

V.   Solution

Perform one of the following:

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

Afterwards, reboot the system.

2) 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

Afterwards, reboot the system.

3) 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 11.2]
# fetch https://security.FreeBSD.org/patches/EN-18:13/icmp.patch
# fetch https://security.FreeBSD.org/patches/EN-18:13/icmp.patch.asc
# gpg --verify icmp.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/11/                                                        r340268
releng/11.2/                                                      r341089
- -------------------------------------------------------------------------

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

<other info on the problem>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-17156>

<URL:https://www.reddit.com/r/BSD/comments/9v6xwg/remotely_triggerable_icmp_buffer_underwrite_in/>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:13.icmp.asc>
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