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=============================================================================
FreeBSD-SA-01:53 Security Advisory
FreeBSD, Inc.

Topic: ipfw `me' on P2P interfaces matches remote address

Category: core
Module: ipfw
Announced: 2001-08-17
Credits: Igor M Podlesny <[email protected]>
Affects: FreeBSD 4-STABLE after February 20, 2001 and prior
to the correction date
FreeBSD 4.3-RELEASE
Corrected: 2001-07-17 10:50:01 UTC (FreeBSD 4.3-STABLE)
2001-07-18 06:56:23 UTC (RELENG_4_3)
FreeBSD only: YES

I. Background

ipfw is a system facility which allows IP packet filtering,
redirecting, and traffic accounting. ipfw `me' rules are filter rules
that specify a source or destination address of `me', intended to
match any IP address configured on a local interface.

II. Problem Description

A flaw in the implementation of the ipfw `me' rules when used in
conjunction with point-to-point interfaces results in filter rules
which match the remote IP address of the point-to-point interface in
addition to the intended local IP address.

III. Impact

IP datagrams with a source or destination IP address of a remote
point-to-point link may be handled in a way unintended by the system
administrator.

For example, given an interface such as

tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500
inet 1.1.1.1 –> 2.2.2.2 netmask 0xff000000

and this ipfw rule:

00010 allow ip from me to any

packets with a source address of 2.2.2.2 would be allowed to pass when
the administrator may have reasonably expected it not to match this
rule.

IV. Workaround

Do not use ipfw `me' rules. Rewrite any existing `me' rules to use
explicit IP addresses.

V. Solution

One of the following:

1) Upgrade your vulnerable FreeBSD system to 4.3-STABLE or the
RELENG_4_3 security branch after the respective correction dates.

2) FreeBSD 4.x systems prior to the correction date:

The following patches have been verified to apply to FreeBSD
4.3-RELEASE and 4-STABLE dated prior to the correction date.

Download the patch and the detached PGP signature from the following
locations, and verify the signature using your PGP utility.

fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:53/ipfw.patch

fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:53/ipfw.patch.asc

cd /usr/src

patch -p < /path/to/patch

install -c -m 0444 -o root -g wheel /usr/src/sys/netinet/in_var.h

/usr/include/netinet/

cd /usr/src/sbin/ipfw

make depend && make all install

The following steps will be different depending upon whether your
system has ipfw compiled into the kernel or is using the ipfw KLD. If
the output of `kldstat' includes `ipfw.ko', then you are using the KLD
and should follow the directions listed in (2a) below. Otherwise, if
your kernel configuration file contains the line `options IPFIREWALL',
you should follow the directions listed in (2b) below.

2a) Execute the following commands as root:

cd /usr/src/sys/modules/ipfw

make depend && make all install

2b) Rebuild and reinstall your kernel as described in
http://www.freebsd.org/handbook/kernelconfig.html

In either case 2a) or 2b), you must reboot your system to load the new
module or kernel.

3) FreeBSD 4.3-RELEASE systems:

An experimental upgrade package is available for users who wish to
provide testing and feedback on the binary upgrade process. This
package may be installed on FreeBSD 4.3-RELEASE systems only, and is
intended for use on systems for which source patching is not practical
or convenient.

If you use the upgrade package, feedback (positive or negative) to
[email protected] is requested so we can improve the
process for future advisories.

During the installation procedure, backup copies are made of the
files which are replaced by the package. These backup copies will
be reinstalled if the package is removed, reverting the system to a
pre-patched state.

fetch

ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-01:53/security-patch-ipfw-01.53.tgz

fetch

ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-01:53/security-patch-ipfw-01.53.tgz.asc

Verify the detached PGP signature using your PGP utility.

pkg_add security-patch-ipfw-01:53.tgz

Restart your system after applying the patch.

VI. Correction details

The following list contains the $FreeBSD$ revision numbers of each
file that was corrected, for the supported branches of FreeBSD. The
$FreeBSD$ revision of installed sources can be examined using the
ident(1) command.

[FreeBSD 4.3-STABLE]

Revision Path
1.33.4.1 src/sys/netinet/in_var.h

[RELENG_4_3]

Revision Path
1.33.2.2 src/sys/netinet/in_var.h

VII. References

<URL:http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/in_var.h#rev1.39&gt;
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