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

Topic:          Incorrect key usage in AES-XCBC-MAC

Category:       core
Module:         netinet6
Announced:      2005-07-27
Credits:        Yukiyo Akisada, Yokogawa Electric Corporation
Affects:        FreeBSD 5.3, FreeBSD 5.4
Corrected:      2005-07-27 08:41:44 UTC (RELENG_6, 6.0-BETA2)
                2005-07-27 08:41:56 UTC (RELENG_5, 5.4-STABLE)
                2005-07-27 08:42:16 UTC (RELENG_5_4, 5.4-RELEASE-p6)
                2005-07-27 08:42:38 UTC (RELENG_5_3, 5.3-RELEASE-p20)
CVE Name:       CAN-2005-2359

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 security protocol for the Internet Protocol networking
layer.  It provides a combination of encryption and authentication of
system, using several possible cryptography algorithms.

II.  Problem Description

A programming error in the implementation of the AES-XCBC-MAC algorithm
for authentication resulted in a constant key being used instead of the
key specified by the system administrator.

III. Impact

If the AES-XCBC-MAC algorithm is used for authentication in the absence
of any encryption, then an attacker may be able to forge packets which
appear to originate from a different system and thereby succeed in
establishing an IPsec session.  If access to sensitive information or
systems is controlled based on the identity of the source system, this
may result in information disclosure or privilege escalation.

IV.  Workaround

Do not use the AES-XCBC-MAC algorithm for authentication, or use it
together with some form of IPsec encryption.

Systems which do not use IPsec, use other algorithms, or have IPsec
encryption enabled are unaffected by this issue.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 5-STABLE, or to the 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 and 5.4
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-05:19/ipsec.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:19/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_5
  src/sys/netinet6/ah_aesxcbcmac.c                                1.1.4.2
RELENG_5_4
  src/UPDATING                                            1.342.2.24.2.15
  src/sys/conf/newvers.sh                                  1.62.2.18.2.11
  src/sys/netinet6/ah_aesxcbcmac.c                            1.1.4.1.2.1
RELENG_5_3
  src/UPDATING                                            1.342.2.13.2.23
  src/sys/conf/newvers.sh                                  1.62.2.15.2.25
  src/sys/netinet6/ah_aesxcbcmac.c                                1.1.6.1
RELENG_6
  src/sys/netinet6/ah_aesxcbcmac.c                                1.2.2.1
- -------------------------------------------------------------------------

VII. References

http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2359

The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:19.ipsec.asc
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