FreeBSD : pycrypto -- vulnerable ElGamal key generation (f45c0049-be72-11e1-a284-0023ae8e59f0)

2012-06-26T00:00:00
ID FREEBSD_PKG_F45C0049BE7211E1A2840023AE8E59F0.NASL
Type nessus
Reporter Tenable
Modified 2013-06-22T00:00:00

Description

Dwayne C. Litzenberger of PyCrypto reports :

In the ElGamal schemes (for both encryption and signatures), g is supposed to be the generator of the entire Z^_p group. However, in PyCrypto 2.5 and earlier, g is more simply the generator of a random sub-group of Z^_p.

The result is that the signature space (when the key is used for signing) or the public key space (when the key is used for encryption) may be greatly reduced from its expected size of log(p) bits, possibly down to 1 bit (the worst case if the order of g is 2).

While it has not been confirmed, it has also been suggested that an attacker might be able to use this fact to determine the private key.

Anyone using ElGamal keys should generate new keys as soon as practical.

Any additional information about this bug will be tracked at https://bugs.launchpad.net/pycrypto/+bug/985164

                                        
                                            #
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were  
# extracted from the FreeBSD VuXML database :
#
# Copyright 2003-2013 Jacques Vidrine and contributors
#
# Redistribution and use in source (VuXML) and 'compiled' forms (SGML,
# HTML, PDF, PostScript, RTF and so forth) with or without modification,
# are permitted provided that the following conditions are met:
# 1. Redistributions of source code (VuXML) must retain the above
#    copyright notice, this list of conditions and the following
#    disclaimer as the first lines of this file unmodified.
# 2. Redistributions in compiled form (transformed to other DTDs,
#    published online in any format, converted to PDF, PostScript,
#    RTF and other formats) must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer
#    in the documentation and/or other materials provided with the
#    distribution.
# 
# THIS DOCUMENTATION IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
# BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
# OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
# OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
# BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
# OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS DOCUMENTATION,
# EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

include("compat.inc");

if (description)
{
  script_id(59700);
  script_version("$Revision: 1.2 $");
  script_cvs_date("$Date: 2013/06/22 00:15:01 $");

  script_cve_id("CVE-2012-2417");

  script_name(english:"FreeBSD : pycrypto -- vulnerable ElGamal key generation (f45c0049-be72-11e1-a284-0023ae8e59f0)");
  script_summary(english:"Checks for updated package in pkg_info output");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote FreeBSD host is missing a security-related update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"Dwayne C. Litzenberger of PyCrypto reports :

In the ElGamal schemes (for both encryption and signatures), g is
supposed to be the generator of the entire Z^*_p group. However, in
PyCrypto 2.5 and earlier, g is more simply the generator of a random
sub-group of Z^*_p.

The result is that the signature space (when the key is used for
signing) or the public key space (when the key is used for encryption)
may be greatly reduced from its expected size of log(p) bits, possibly
down to 1 bit (the worst case if the order of g is 2).

While it has not been confirmed, it has also been suggested that an
attacker might be able to use this fact to determine the private key.

Anyone using ElGamal keys should generate new keys as soon as
practical.

Any additional information about this bug will be tracked at
https://bugs.launchpad.net/pycrypto/+bug/985164"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"http://lists.dlitz.net/pipermail/pycrypto/2012q2/000587.html"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugs.launchpad.net/pycrypto/+bug/985164"
  );
  # http://www.freebsd.org/ports/portaudit/f45c0049-be72-11e1-a284-0023ae8e59f0.html
  script_set_attribute(
    attribute:"see_also",
    value:"http://www.nessus.org/u?12cbf641"
  );
  script_set_attribute(attribute:"solution", value:"Update the affected package.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:freebsd:freebsd:py-pycrypto");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:freebsd:freebsd");

  script_set_attribute(attribute:"vuln_publication_date", value:"2012/05/24");
  script_set_attribute(attribute:"patch_publication_date", value:"2012/06/24");
  script_set_attribute(attribute:"plugin_publication_date", value:"2012/06/26");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2012-2013 Tenable Network Security, Inc.");
  script_family(english:"FreeBSD Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/FreeBSD/release", "Host/FreeBSD/pkg_info");

  exit(0);
}


include("audit.inc");
include("freebsd_package.inc");


if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (!get_kb_item("Host/FreeBSD/release")) audit(AUDIT_OS_NOT, "FreeBSD");
if (!get_kb_item("Host/FreeBSD/pkg_info")) audit(AUDIT_PACKAGE_LIST_MISSING);


flag = 0;

if (pkg_test(save_report:TRUE, pkg:"py-pycrypto>=2.5<2.6")) flag++;

if (flag)
{
  if (report_verbosity > 0) security_warning(port:0, extra:pkg_report_get());
  else security_warning(0);
  exit(0);
}
else audit(AUDIT_HOST_NOT, "affected");