TCP reassembly vulnerability in Freebsd

=============================================================================
FreeBSD-SA-14:08.tcp                                        Security Advisory
                                                          The FreeBSD Project

Topic:          TCP reassembly vulnerability

Category:       core
Module:         inet
Announced:      2014-04-30
Credits:        Jonathan Looney
Affects:        All supported versions of FreeBSD.
Corrected:      2014-04-30 04:04:20 UTC (stable/8, 8.4-STABLE)
                2014-04-30 04:05:47 UTC (releng/8.4, 8.4-RELEASE-p9)
                2014-04-30 04:05:47 UTC (releng/8.3, 8.3-RELEASE-p16)
                2014-04-30 04:04:20 UTC (stable/9, 9.2-STABLE)
                2014-04-30 04:05:47 UTC (releng/9.2, 9.2-RELEASE-p5)
                2014-04-30 04:05:47 UTC (releng/9.1, 9.1-RELEASE-p12)
                2014-04-30 04:03:05 UTC (stable/10, 10.0-STABLE)
                2014-04-30 04:04:42 UTC (releng/10.0, 10.0-RELEASE-p2)
CVE Name:       CVE-2014-3000

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

I.   Background

The Transmission Control Protocol (TCP) of the TCP/IP protocol suite
provides a connection-oriented, reliable, sequence-preserving data
stream service.  When network packets making up a TCP stream (``TCP
segments'') are received out-of-sequence, they are maintained in a
reassembly queue by the destination system until they can be re-ordered
and re-assembled.

II.  Problem Description

FreeBSD may add a reassemble queue entry on the stack into the segment list
when the reassembly queue reaches its limit.  The memory from the stack is
undefined after the function returns.  Subsequent iterations of the
reassembly function will attempt to access this entry.

III. Impact

An attacker who can send a series of specifically crafted packets with a
connection could cause a denial of service situation by causing the kernel
to crash.

Additionally, because the undefined on stack memory may be overwritten by
other kernel threads, while extremely difficult, it may be possible for
an attacker to construct a carefully crafted attack to obtain portion of
kernel memory via a connected socket.  This may result in the disclosure of
sensitive information such as login credentials, etc. before or even
without crashing the system.

IV.  Workaround

It is possible to defend to these attacks by doing traffic normalization
using a firewall.  This can be done by including the following /etc/pf.conf
configuration:

 scrub in all

This requires pf(4) to be enabled, and have the mentioned configuration
loaded.

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.

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.

# fetch http://security.FreeBSD.org/patches/SA-14:08/tcp.patch
# fetch http://security.FreeBSD.org/patches/SA-14:08/tcp.patch.asc
# gpg --verify tcp.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) 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

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/8/                                                         r265123
releng/8.3/                                                       r265125
releng/8.4/                                                       r265125
stable/9/                                                         r265123
releng/9.1/                                                       r265125
releng/9.2/                                                       r265125
stable/10/                                                        r265122
releng/10.0/                                                      r265124
- -------------------------------------------------------------------------

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:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-3000>

The latest revision of this advisory is available at
<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-14:08.tcp.asc>