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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD pf(4) Scrub Rule Error Lets Remote Users Deny Service
SecurityTracker Alert ID:  1015542
SecurityTracker URL:  http://securitytracker.com/id/1015542
CVE Reference:   CVE-2006-0381   (Links to External Site)
Date:  Jan 25 2006
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 5.3, 5.4, 6.0
Description:   A vulnerability was reported in FreeBSD in the pf(4) packet filter function. A remote user can cause the kernel to crash.

A remote user can send specially crafted IP packet fragments to trigger a logic error in writing to the pf IP fragment cache when the 'scrub fragment crop' or 'scrub fragment drop-ovl' rules are used. The packet fragment may be inserted twice, causing the kernel to crash.

Systems that do not use pf are not affected.

Systems that do not use the 'scrub fragment crop' or 'scrub fragment drop-ovl' pf rules are also not affected.

The vendor credits Jakob Schlyter and Daniel Hartmeier with reporting this vulnerability.

Impact:   A remote user can cause the kernel to crash.
Solution:   The vendor has provided the following solution information [quoted]:

Perform one of the following:

1) Upgrade your vulnerable system to 5-STABLE or 6-STABLE, or to the
RELENG_6_0, RELENG_5_4, or RELENG_5_3 security branch dated after the
correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 5.3, 5.4,
and 6.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:07/pf.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:07/pf.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.

The vendor's advisory is available at:

ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-06:07.pf.asc

Vendor URL:  www.freebsd.org/security/ (Links to External Site)
Cause:   State error

Message History:   This archive entry has one or more follow-up message(s) listed below.
Mar 30 2006 (NetBSD Issues Fix) FreeBSD pf(4) Scrub Rule Error Lets Remote Users Deny Service
NetBSD has released a fix.



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-06:07.pf

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

=============================================================================
FreeBSD-SA-06:07.pf                                         Security Advisory
                                                          The FreeBSD Project

Topic:          IP fragment handling panic in pf(4)

Category:       contrib
Module:         sys_contrib
Announced:      2006-01-25
Credits:        Jakob Schlyter, Daniel Hartmeier
Affects:        FreeBSD 5.3, FreeBSD 5.4, and FreeBSD 6.0
Corrected:      2006-01-25 10:00:59 UTC (RELENG_6, 6.0-STABLE)
                2006-01-25 10:01:26 UTC (RELENG_6_0, 6.0-RELEASE-p4)
                2006-01-25 10:01:47 UTC (RELENG_5, 5.4-STABLE)
                2006-01-25 10:02:07 UTC (RELENG_5_4, 5.4-RELEASE-p10)
                2006-01-25 10:02:27 UTC (RELENG_5_3, 5.3-RELEASE-p25)
CVE Name:       CVE-2006-0381

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

I.   Background

pf 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 logic bug in pf's IP fragment cache may result in a packet fragment
being inserted twice, violating a kernel invariant.

III. Impact

By sending carefully crafted sequence of IP packet fragments, a remote
attacker can cause a system running pf with a ruleset containing a
'scrub fragment crop' or 'scrub fragment drop-ovl' rule to crash.

IV.  Workaround

Do not use 'scrub fragment crop' or 'scrub fragment drop-ovl' rules
on systems running pf.  In most cases, such rules can be replaced by
'scrub fragment reassemble' rules; see the pf.conf(5) manual page for
more details.

Systems which do not use pf, or use pf but do not use the aforementioned
rules, are not affected by this issue.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 5-STABLE or 6-STABLE, or to the
RELENG_6_0, RELENG_5_4, or RELENG_5_3 security branch dated after the
correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 5.3, 5.4,
and 6.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:07/pf.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:07/pf.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.

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_5
  src/sys/contrib/pf/net/pf_norm.c                               1.10.2.2
RELENG_5_4
  src/UPDATING                                            1.342.2.24.2.19
  src/sys/conf/newvers.sh                                  1.62.2.18.2.15
  src/sys/contrib/pf/net/pf_norm.c                               1.10.6.1
RELENG_5_3
  src/UPDATING                                            1.342.2.13.2.28
  src/sys/conf/newvers.sh                                  1.62.2.15.2.30
  src/sys/contrib/pf/net/pf_norm.c                               1.10.4.1
RELENG_6
  src/sys/contrib/pf/net/pf_norm.c                               1.11.2.3
RELENG_6_0
  src/UPDATING                                              1.416.2.3.2.9
  src/sys/conf/newvers.sh                                    1.69.2.8.2.5
  src/sys/contrib/pf/net/pf_norm.c                           1.11.2.1.2.1
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0381

The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-06:07.pf.asc
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