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FreeBSD-SA-19:05.pf Security Advisory
The FreeBSD Project

Topic: IPv6 fragment reassembly panic in pf(4)

Category: contrib
Module: pf
Announced: 2019-05-14
Credits: Synacktiv
Affects: All supported versions of FreeBSD
Corrected: 2019-03-01 18:12:05 UTC (stable/12, 12.0-STABLE)
2019-05-14 23:10:21 UTC (releng/12.0, 12.0-RELEASE-p4)
2019-03-01 18:12:07 UTC (stable/11, 11.3-PRERELEASE)
2019-05-14 23:10:21 UTC (releng/11.2, 11.2-RELEASE-p10)
CVE Name: CVE-2019-5597

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

pf(4) is an Internet Protocol packet filter originally written for OpenBSD.
In addition to filtering packets, it also has packet normalization
capabilities.

II. Problem Description

A bug in the pf(4) IPv6 fragment reassembly logic incorrectly uses the last
extension header offset from the last received packet instead of from the
first packet.

III. Impact

Malicious IPv6 packets with different IPv6 extensions could cause a kernel
panic or potentially a filtering rule bypass.

IV. Workaround

Only systems leveraging the pf(4) firewall and include packet scrubbing using
the recommended ‘scrub all in’ or similar are affected.

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.
Afterwards, 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

Afterwards, 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-19:05/pf.patch
# fetch https://security.FreeBSD.org/patches/SA-19:05/pf.patch.asc
# gpg –verify pf.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/ r344706
releng/12.0/ r347591
stable/11/ r344707
releng/11.2/ r347591
– ————————————————————————-

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://www.synacktiv.com/ressources/Synacktiv_OpenBSD_PacketFilter_CVE-2019-5597_ipv6_frag.pdf>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-5597>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:05.pf.asc>
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