OpenSSH < 10.6p2 Authentication Bypass

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
##

include('compat.inc');

if (description)
{
  script_id(377050);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/11/06");

  script_cve_id("CVE-2026-123158");

  script_name(english:"OpenSSH < 10.6p2 Authentication Bypass");

  script_set_attribute(attribute:"synopsis", value:
"The SSH server running on the remote host is affected by an authentication bypass vulnerability.");
  script_set_attribute(attribute:"description", value:
"The version of OpenSSH installed on the remote host is prior to 10.6p2. It is, therefore, affected by an
authentication bypass vulnerability as referenced in the release-10.6p2 advisory.

  - sshd in OpenSSH before 10.6p2 on Linux, when musl libc is used without PAM, lacks a workaround for a
    password authentication bypass (related to misinterpretation of whether a string is intended to be a
    password hash). For some configurations of accounts, any password between 256 and 1024 characters
    succeeds. An example of a platform using musl libc without PAM is Alpine Linux. (CVE-2026-123158)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version
number.");
  # https://www.alpinelinux.org/posts/2026-11-05-openssh-password-authentication-bypass/
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?a448912e");
  script_set_attribute(attribute:"see_also", value:"https://www.openssh.com/txt/release-10.6p2");
  script_set_attribute(attribute:"solution", value:
"Upgrade to OpenSSH version 10.6p2 or later.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:H/Au:N/C:C/I:C/A:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-123158");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/11/05");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/11/05");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/11/06");

  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) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("openssh_detect.nbin");
  script_require_keys("installed_sw/OpenSSH");
  script_require_ports("Services/ssh", 22);

  exit(0);
}

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

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_version': '10.6p2'}
];

# Only musl libc builds with PAM disabled and password authentication enabled are affected, and the SSH banner
# reveals none of these, so require paranoia
vcf::openssh::check_version_and_report(
  app_info:app_info,
  constraints:constraints,
  severity:SECURITY_HOLE,
  require_paranoia:TRUE
);