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FreeBSD-SA-06:19.openssl                                    Security Advisory
                                                          The FreeBSD Project

Topic:          Incorrect PKCS#1 v1.5 padding validation in crypto(3)

Category:       contrib
Module:         openssl
Announced:      2006-09-06
Affects:        All FreeBSD releases.
Corrected:      2006-09-06 21:18:26 UTC (RELENG_6, 6.1-STABLE)
                2006-09-06 21:19:21 UTC (RELENG_6_1, 6.1-RELEASE-p6)
                2006-09-06 21:20:08 UTC (RELENG_6_0, 6.0-RELEASE-p11)
                2006-09-06 21:20:54 UTC (RELENG_5, 5.5-STABLE)
                2006-09-06 21:21:50 UTC (RELENG_5_5, 5.5-RELEASE-p4)
                2006-09-06 21:22:39 UTC (RELENG_5_4, 5.4-RELEASE-p18)
                2006-09-06 21:23:16 UTC (RELENG_5_3, 5.3-RELEASE-p33)
                2006-09-06 21:24:04 UTC (RELENG_4, 4.11-STABLE)
                2006-09-06 21:24:54 UTC (RELENG_4_11, 4.11-RELEASE-p21)
CVE Name:       CVE-2006-4339

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

FreeBSD includes software from the OpenSSL Project.  The OpenSSL Project is
a collaborative effort to develop a robust, commercial-grade, full-featured,
and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3)
and Transport Layer Security (TLS v1) protocols as well as a full-strength
general purpose cryptography library.

PKCS#1 v1.5 is a standard for "padding" data before performing a
cryptographic operation using the RSA algorithm.  PKCS#1 v1.5 signatures
are for example used in X.509 certificates.

RSA public keys may use a variety of public exponents, of which 3, 17, and
65537 are most common.  As a result of a number of known attacks, most keys
generated recently use a public exponent of at least 65537.

II.  Problem Description

When verifying a PKCS#1 v1.5 signature, OpenSSL ignores any bytes which
follow the cryptographic hash being signed.  In a valid signature there
will be no such bytes.

III. Impact

OpenSSL will incorrectly report some invalid signatures as valid.  When
an RSA public exponent of 3 is used, or more generally when a small public
exponent is used with a relatively large modulus (e.g., a public exponent
of 17 with a 4096-bit modulus), an attacker can construct a signature which
OpenSSL will accept as a valid PKCS#1 v1.5 signature.

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_1, RELENG_6_0, RELENG_5_5, RELENG_5_4, RELENG_5_3,
or RELENG_4_11 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.11, 5.3,
5.4, 5.5, 6.0, and 6.1 systems.

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-06:19/openssl.patch
# fetch http://security.FreeBSD.org/patches/SA-06:19/openssl.patch.asc

b) Execute the following commands as root:

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

c) Recompile the operating system as described in
<URL: http://www.freebsd.org/handbook/makeworld.html> and reboot the
system.

NOTE: Any third-party applications, including those installed from the
FreeBSD ports collection, which are statically linked to libcrypto(3)
should be recompiled in order to use the corrected code.

VI.  Correction details

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

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_4
  src/crypto/openssl/crypto/rsa/rsa_sign.c                    1.1.1.1.2.6
RELENG_4_11
  src/UPDATING                                             1.73.2.91.2.22
  src/sys/conf/newvers.sh                                  1.44.2.39.2.25
  src/crypto/openssl/crypto/rsa/rsa_sign.c                1.1.1.1.2.5.6.1
RELENG_5
  src/crypto/openssl/crypto/rsa/rsa_sign.c                    1.1.1.6.4.1
RELENG_5_5
  src/UPDATING                                             1.342.2.35.2.4
  src/sys/conf/newvers.sh                                   1.62.2.21.2.6
  src/crypto/openssl/crypto/rsa/rsa_sign.c                   1.1.1.6.16.1
RELENG_5_4
  src/UPDATING                                            1.342.2.24.2.27
  src/sys/conf/newvers.sh                                  1.62.2.18.2.23
  src/crypto/openssl/crypto/rsa/rsa_sign.c                    1.1.1.6.8.1
RELENG_5_3
  src/UPDATING                                            1.342.2.13.2.36
  src/sys/conf/newvers.sh                                  1.62.2.15.2.38
  src/crypto/openssl/crypto/rsa/rsa_sign.c                    1.1.1.6.6.1
RELENG_6
  src/crypto/openssl/crypto/rsa/rsa_sign.c                   1.1.1.6.10.1
RELENG_6_1
  src/UPDATING                                             1.416.2.22.2.8
  src/sys/conf/newvers.sh                                   1.69.2.11.2.8
  src/crypto/openssl/crypto/rsa/rsa_sign.c                   1.1.1.6.14.1
RELENG_6_0
  src/UPDATING                                             1.416.2.3.2.16
  src/sys/conf/newvers.sh                                   1.69.2.8.2.12
  src/crypto/openssl/crypto/rsa/rsa_sign.c                   1.1.1.6.12.1
- -------------------------------------------------------------------------

VII. References

http://www.openssl.org/news/secadv_20060905.txt
http://www.imc.org/ietf-openpgp/mail-archive/msg14307.html
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-4339

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-06:19.openssl.asc
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