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Category:   Application (Security)  >   IPSec Vendors:   FreeBSD
(FreeBSD Issues Fix) IPSec Bug in 'xform_esp.c' May Let Remote Users Bypass Anti-Replay Sequence Number Checking
SecurityTracker Alert ID:  1015811
SecurityTracker URL:  http://securitytracker.com/id/1015811
CVE Reference:   CVE-2006-0905   (Links to External Site)
Date:  Mar 23 2006
Impact:   Modification of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in IPSec. A remote user may be able to bypass the anti-replay mechanism.

There is a programming error in the fast_ipsec(4) implementation in FreeBSD (and possibly other implementations) that does not properly track sequence numbers and, as a result, sequence numbers with a Security Association are not updated. This allows packets to unconditionally pass the sequence number verification checks.

The vulnerability resides in 'xform_esp.c'.

Pawel Jakub Dawidek discovered this vulnerability.

Impact:   A remote user may be able to bypass the anti-replay sequence number checking mechanism.
Solution:   FreeBSD has released a fix and has provided the following solution instructions [quoted]:

Perform one of the following:

1) Upgrade your vulnerable system to 4-STABLE, 5-STABLE, or 6-STABLE,
or to the RELENG_6_0, RELENG_5_4, RELENG_5_3, RELENG_4_11, or
RELENG_4_10 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.10,
4.11, 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-06:11/ipsec.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:11/ipsec.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 FreeBSD advisory is available at:

ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-06:11.ipsec.asc

Vendor URL:  www.freebsd.org/ (Links to External Site)
Cause:   State error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  4.8 - 6.1

Message History:   This archive entry is a follow-up to the message listed below.
Mar 23 2006 IPSec Bug in 'xform_esp.c' May Let Remote Users Bypass Anti-Replay Sequence Number Checking



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-06:11.ipsec


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

=============================================================================
FreeBSD-SA-06:11.ipsec                                      Security Advisory
                                                          The FreeBSD Project

Topic:          IPsec replay attack vulnerability

Category:       core
Module:         sys_netipsec
Announced:      2006-03-22
Credits:        Pawel Jakub Dawidek
Affects:        All FreeBSD releases since 4.8-RELEASE
Corrected:      2006-03-22 16:01:08 UTC (RELENG_6, 6.1-STABLE)
                2006-03-22 16:01:38 UTC (RELENG_6_0, 6.0-RELEASE-p6)
                2006-03-22 16:01:56 UTC (RELENG_5, 5.5-STABLE)
                2006-03-22 16:02:17 UTC (RELENG_5_4, 5.4-RELEASE-p13)
                2006-03-22 16:02:35 UTC (RELENG_5_3, 5.3-RELEASE-p28)
                2006-03-22 16:02:49 UTC (RELENG_4, 4.11-STABLE)
                2006-03-22 16:03:05 UTC (RELENG_4_11, 4.11-RELEASE-p16)
                2006-03-22 16:03:25 UTC (RELENG_4_10, 4.10-RELEASE-p22)
CVE Name:       CVE-2006-0905

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

IPsec is a set of protocols, including ESP (Encapsulating Security Payload)
and AH (Authentication Header), that provide security services for IP
datagrams.  ESP protects IP payloads from wire-tapping by encrypting them
using secret key cryptography algorithms.  AH guarantees the integrity of IP
packets and protects them from intermediate alteration or impersonation by
attaching a cryptographic checksum computed using one-way hash functions.

II.  Problem Description

IPsec provides an anti-replay service which when enabled prevents an attacker
from successfully executing a replay attack.  This is done through the
verification of sequence numbers.  A programming error in the fast_ipsec(4)
implementation results in the sequence number associated with a Security
Association not being updated, allowing packets to unconditionally pass
sequence number verification checks.

III. Impact

An attacker able to to intercept IPSec packets can replay them.  If higher
level protocols which do not provide any protection against packet replays
(e.g., UDP) are used, this may have a variety of effects.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 4-STABLE, 5-STABLE, or 6-STABLE,
or to the RELENG_6_0, RELENG_5_4, RELENG_5_3, RELENG_4_11, or
RELENG_4_10 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.10,
4.11, 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-06:11/ipsec.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:11/ipsec.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_4
  src/sys/netipsec/xform_esp.c                                    1.2.2.4
RELENG_4_11
  src/UPDATING                                             1.73.2.91.2.17
  src/sys/conf/newvers.sh                                  1.44.2.39.2.20
  src/sys/netipsec/xform_esp.c                                1.2.2.3.6.1
RELENG_4_10
  src/UPDATING                                             1.73.2.90.2.23
  src/sys/conf/newvers.sh                                  1.33.2.34.2.24
  src/sys/netipsec/xform_esp.c                                1.2.2.3.4.1
RELENG_5
  src/sys/netipsec/xform_esp.c                                    1.9.2.2
RELENG_5_4
  src/UPDATING                                            1.342.2.24.2.22
  src/sys/conf/newvers.sh                                  1.62.2.18.2.18
  src/sys/netipsec/xform_esp.c                                1.9.2.1.2.1
RELENG_5_3
  src/UPDATING                                            1.342.2.13.2.31
  src/sys/conf/newvers.sh                                  1.62.2.15.2.33
  src/sys/netipsec/xform_esp.c                                    1.9.4.1
RELENG_6
  src/sys/netipsec/xform_esp.c                                   1.10.2.1
RELENG_6_0
  src/UPDATING                                             1.416.2.3.2.11
  src/sys/conf/newvers.sh                                    1.69.2.8.2.7
  src/sys/netipsec/xform_esp.c                                   1.10.4.1
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0905

The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-06:11.ipsec.asc
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