Vulnerabilities > CVE-2006-2369 - Improper Authentication vulnerability in VNC Realvnc 4.1.1

• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-2369
• http://en.wikipedia.org/wiki/RFB
• http://en.wikipedia.org/wiki/Vnc

• http://secunia.com/advisories/20107/
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-2369

#
# (C) Tenable Network Security, Inc.
#

include("compat.inc");

if (description) {
  script_id(21564);
  script_version("1.30");
  script_cvs_date("Date: 2018/07/25 18:58:04");

  script_cve_id("CVE-2006-2369", "CVE-2006-2450");
  script_bugtraq_id(17978, 18977);
  script_xref(name:"CERT", value:"117929");
  script_xref(name:"EDB-ID", value:"1791");

  script_name(english:"VNC Security Type Enforcement Failure Remote Authentication Bypass");
  script_summary(english:"Tries to bypass authentication using a type of None.");

 script_set_attribute(attribute:"synopsis", value:
"The remote VNC server is affected by multiple authentication bypass
vulnerabilities.");
 script_set_attribute(attribute:"description", value:
"The version of VNC server running on the remote host is affected by
the following vulnerabilities :

  - A flaw exists in RealVNC due to an error when handling
    password authentication. A remote attacker can exploit
    this to bypass authentication by using a specially
    crafted request in which the client specifies an
    insecure security type (e.g., 'Type 1 - None'), which is
    accepted even if not offered by the server.
    (CVE-2006-2369)

  - A flaw exists in LibVNCServer within file auth.c due to
    an error when handling password authentication. A remote
    attacker can exploit this to bypass authentication by
    using a specially crafted request in which the client
    specifies an insecure security type (e.g., 'Type 1 -
    None'), which is accepted even if not offered by the
    server. (CVE-2006-2450)");
  # http://www.intelliadmin.com/index.php/2006/05/security-flaw-in-realvnc-411/
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?ef2b8a64" );
  # https://web.archive.org/web/20060623010008/http://www.realvnc.com/products/free/4.1/release-notes.html
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?8a2c16a0");
  # https://web.archive.org/web/20060623010103/http://www.realvnc.com/products/personal/4.2/release-notes.html
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?b218067e");
  # https://web.archive.org/web/20060623010019/http://www.realvnc.com/products/enterprise/4.2/release-notes.html
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?519d872d");
  script_set_attribute(attribute:"see_also", value:"https://github.com/LibVNC/libvncserver");
  script_set_attribute(attribute:"solution", value:
"If using RealVNC, upgrade to RealVNC Free Edition 4.1.2 / Personal
Edition 4.2.3 / Enterprise Edition 4.2.3 or later.

If using LibVNCServer, upgrade to version 0.8.2 or later.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:F/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:F/RL:O/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");
  script_set_attribute(attribute:"exploit_framework_core", value:"true");
  script_set_attribute(attribute:"exploit_framework_canvas", value:"true");
  script_set_attribute(attribute:"canvas_package", value:'CANVAS');

  script_set_attribute(attribute:"vuln_publication_date", value: "2006/05/15");
  script_set_attribute(attribute:"patch_publication_date", value: "2006/06/23");
  script_set_attribute(attribute:"plugin_publication_date", value: "2006/05/15");

  script_set_attribute(attribute:"plugin_type", value:"remote");
  script_set_attribute(attribute:"cpe",value:"cpe:/a:vnc:realvnc");
  script_set_attribute(attribute:"cpe",value:"cpe:/a:libvncserver:libvncserver");
  script_end_attributes();

  script_category(ACT_ATTACK);
  script_family(english:"Misc.");

  script_copyright(english:"This script is Copyright (C) 2006-2018 Tenable Network Security, Inc.");

  script_dependencies("vnc.nasl");
  script_require_ports("Services/vnc", 5900);

  exit(0);
}

include("audit.inc");
include("byte_func.inc");
include("global_settings.inc");
include("misc_func.inc");

protocol = "VNC Service";
port = get_kb_item("Services/vnc");
if (!port) port = 5900;
if (!get_port_state(port)) audit(AUDIT_PORT_CLOSED, port);

# Establish a connection.
soc = open_sock_tcp(port);
if (!soc) audit(AUDIT_SOCK_FAIL, port);

# nb: The RFB protocol is described at:
#     http://www.realvnc.com/docs/rfbproto.pdf


# Get the protocol version supported by the server.
s = recv(socket:soc, length:512, min:12);
if (empty_or_null(s) || strlen(s) < 12)
{
  close(soc);
  audit(AUDIT_NO_BANNER, port);
}

v = pregmatch(pattern:'^RFB ([0-9]+)\\.([0-9]+)\n', string:s);
if (empty_or_null(v))
{
  close(soc);
  audit(AUDIT_NO_BANNER, port);
}
ver_major = int(v[1]);
ver_minor = int(v[2]);

# nb: protocol versions before 3.7 don't allow the
#     client to select the authentication type.
if (ver_major != 3 || ver_minor < 7)
{
  close(soc);
  audit(AUDIT_INST_VER_NOT_VULN, protocol);
}

# Reply with same version.
send(socket:soc, data:s);

# Read the security types supported by the server.
types = NULL;
set_byte_order(BYTE_ORDER_BIG_ENDIAN);
s = recv(socket:soc, length:1, min:1);

if (empty_or_null(s))
{
  close(soc);
  audit(AUDIT_SOCK_FAIL, port);
}

if (strlen(s) == 1)
{
  n = ord(s);
  if (n > 0)
  {
    for (i=0; i<n; i++)
    {
      s = recv(socket:soc, length:1, min:1);
      if (empty_or_null(s))
      {
        close(soc);
        audit(AUDIT_SOCK_FAIL, port);
      }
      if (isnull(types)) types = make_list(ord(s));
      else types = make_list(types, ord(s));
    }
  }
}


if (types)
{
  # Make sure authentication is required.
  auth_required = 1;
  foreach type (types)
    # nb: type == 0 => connection failed.
    if (type == 0) auth_required = 0;
    # nb: type == 1 => None is supported.
    else if (type == 1) auth_required = 0;

  # If it is...
  if (auth_required)
  {
    # Try to bypass authentication.
    send(socket:soc, data:mkbyte(1));

    # If the protocol is below 3.8, send a ClientInit and look for a ServerInit.
    if (ver_minor < 8)
    {
      # Set Shared-Flag to true.
      send(socket:soc, data:mkbyte(1));
      s = recv(socket:soc, length:128);

      # There's a problem if it looks like a ServerInit
      if (! empty_or_null(s)
         && strlen(s) >= 24
         && getdword(blob:s, pos:0x14) + 24 == strlen(s)
      )
      {
        security_hole(port);
      }
      else
      {
        close(soc);
        audit(AUDIT_INST_VER_NOT_VULN, protocol);
      }
    }
    # If the protocol is 3.8, check the SecurityResult message.
    else
    {
      s = recv(socket:soc, min:3, length:8);
      # There's a problem if it's an OK response of four null bytes.
      if (! empty_or_null(s) && s == mkdword(0))
      {
        security_hole(port);
      }
      else
      {
        close(soc);
        audit(AUDIT_INST_VER_NOT_VULN, protocol);
      }
    }
  }
  else
  {
    close(soc);
    audit(AUDIT_INST_VER_NOT_VULN, protocol);
  }
}
else
{
  close(soc);
  audit(AUDIT_INST_VER_NOT_VULN, protocol);
}

close(soc);

#%NASL_MIN_LEVEL 80502
#
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were  
# extracted from the FreeBSD VuXML database :
#
# Copyright 2003-2018 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(21574);
  script_version("1.31");
  script_cvs_date("Date: 2019/08/02 13:32:38");

  script_cve_id("CVE-2006-2369");
  script_bugtraq_id(17978);

  script_name(english:"FreeBSD : vnc -- authentication bypass vulnerability (4645b98c-e46e-11da-9ae7-00123fcc6e5c)");
  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:
"RealVNC is susceptible to an authentication-bypass vulnerability. A
malicious VNC client can cause a VNC server to allow it to connect
without any authentication regardless of the authentication settings
configured in the server. Exploiting this issue allows attackers to
gain unauthenticated, remote access to the VNC servers."
  );
  # http://www.securityfocus.com/archive/1/433994/30/0/threaded
  script_set_attribute(
    attribute:"see_also",
    value:"https://www.securityfocus.com/archive/1/433994/30/0/threaded"
  );
  # https://vuxml.freebsd.org/freebsd/4645b98c-e46e-11da-9ae7-00123fcc6e5c.html
  script_set_attribute(
    attribute:"see_also",
    value:"http://www.nessus.org/u?759aa26c"
  );
  script_set_attribute(attribute:"solution", value:"Update the affected package.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:F/RL:OF/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");
  script_set_attribute(attribute:"exploit_framework_core", value:"true");
  script_set_attribute(attribute:"exploit_framework_canvas", value:"true");
  script_set_attribute(attribute:"canvas_package", value:'CANVAS');

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2006/05/15");
  script_set_attribute(attribute:"patch_publication_date", value:"2006/05/18");
  script_set_attribute(attribute:"plugin_publication_date", value:"2006/05/19");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2006-2019 and is owned by Tenable, Inc. or an Affiliate thereof.");
  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:"vnc=4.1.1")) flag++;

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