OpenSSH S/KEY Authentication Account Enumeration

#
# (C) Tenable, Inc.
#

include('compat.inc');

if (description)
{
  script_id(17704);
  script_version("1.6");
  script_set_attribute(attribute:"plugin_modification_date", value:"2024/03/27");

  script_cve_id("CVE-2007-2243");
  script_bugtraq_id(23601);

  script_name(english:"OpenSSH S/KEY Authentication Account Enumeration");
  script_summary(english:"Checks if OpenSSH is installed.");

  script_set_attribute(attribute:"synopsis", value:
"The remote host is affected by an information disclosure
vulnerability.");
  script_set_attribute(attribute:"description", value:
"When OpenSSH has S/KEY authentication enabled, it is possible to
remotely determine if an account configured for S/KEY authentication
exists. 

Note that Nessus has not attempted to exploit the issue but has
instead only checked if OpenSSH is running on the remote host. As a
result, it will not detect if the remote host has implemented a
workaround.");
# https://web.archive.org/web/20110723143430/http://www.helith.net/txt/openssh_system_account_enumeration_if_s-key_is_used.txt
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?907640b9");
  script_set_attribute(attribute:"solution", value:
"A patch currently does not exist for this issue. As a workaround,
either set 'ChallengeResponseAuthentication' in the OpenSSH config to
'no' or use a version of OpenSSH without S/KEY support compiled in.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:P/I:N/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");
 script_cwe_id(287);

  script_set_attribute(attribute:"vuln_publication_date", value:"2007/04/21");
  script_set_attribute(attribute:"plugin_publication_date", value:"2011/11/18");

  script_set_attribute(attribute:"plugin_type", value:"remote");
  script_set_attribute(attribute:"cpe", value:"cpe:/a:openbsd:openssh");
  script_end_attributes();

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

  script_copyright(english:"This script is Copyright (C) 2023-2024 and is owned by Tenable, Inc. or an Affiliate thereof.");
  
  script_dependencies("openssh_detect.nbin");
  script_require_keys("installed_sw/OpenSSH", "Settings/PCI_DSS");
  script_require_ports("Services/ssh", 22);

  exit(0);
}

include('backport.inc');
include('vcf.inc');
include('vcf_extras.inc');

if (!get_kb_item("Settings/PCI_DSS")) exit(0, "PCI-DSS compliance checking is not enabled.");

var port = get_service(svc:'ssh', default:22, exit_on_fail:TRUE);
var app_info = vcf::openssh::get_app_info(app:'OpenSSH', port:port);

vcf::check_all_backporting(app_info:app_info);

var constraints = [
  {'fixed_display' : 'See vendor advisory'}
];

vcf::openssh::check_version_and_report(app_info:app_info, constraints:constraints, severity:SECURITY_WARNING);