Ubuntu 18.04 LTS / 20.04 LTS / 22.04 LTS : Dropbear vulnerabilities (USN-7292-1)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-7292-1. The text
# itself is copyright (C) Canonical, Inc. See
# <https://ubuntu.com/security/notices>. Ubuntu(R) is a registered
# trademark of Canonical, Inc.
##

include('compat.inc');

if (description)
{
  script_id(216761);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2025/02/25");

  script_cve_id("CVE-2021-36369", "CVE-2023-48795");
  script_xref(name:"USN", value:"7292-1");

  script_name(english:"Ubuntu 18.04 LTS / 20.04 LTS / 22.04 LTS : Dropbear vulnerabilities (USN-7292-1)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Ubuntu host is missing one or more security updates.");
  script_set_attribute(attribute:"description", value:
"The remote Ubuntu 18.04 LTS / 20.04 LTS / 22.04 LTS host has packages installed that are affected by multiple
vulnerabilities as referenced in the USN-7292-1 advisory.

    Manfred Kaiser discovered that Dropbear through 2020.81 does not properly check the available
    authentication methods in the client-side SSH code. An attacker could use this vulnerability to gain
    unauthorized access to remote systems. (CVE-2021-36369)

    Fabian Bumer, Marcus Brinkmann, and Jrg Schwenk discovered that the SSH transport protocol
    implementation in Dropbear had weak integrity checks. An attacker could use this vulnerability to bypass
    security features like encryption and integrity checks. (CVE-2023-48795)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version
number.");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/notices/USN-7292-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected packages.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:N/I:C/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:POC/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:P/RL:O/RC:C");
  script_set_attribute(attribute:"cvss4_vector", value:"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N");
  script_set_attribute(attribute:"cvss4_threat_vector", value:"CVSS:4.0/E:P");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2021-36369");
  script_set_attribute(attribute:"cvss4_score_source", value:"CVE-2023-48795");

  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");

  script_set_attribute(attribute:"vuln_publication_date", value:"2022/10/12");
  script_set_attribute(attribute:"patch_publication_date", value:"2025/02/25");
  script_set_attribute(attribute:"plugin_publication_date", value:"2025/02/25");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:18.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:20.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:22.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:dropbear");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:dropbear-bin");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:dropbear-initramfs");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:dropbear-run");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Ubuntu Local Security Checks");

  script_copyright(english:"Ubuntu Security Notice (C) 2025 Canonical, Inc. / NASL script (C) 2025 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info.nasl", "ubuntu_pro_sub_detect.nasl");
  script_require_keys("Host/cpu", "Host/Ubuntu", "Host/Ubuntu/release", "Host/Debian/dpkg-l");

  exit(0);
}

include('debian_package.inc');

if ( ! get_kb_item('Host/local_checks_enabled') ) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
var os_release = get_kb_item('Host/Ubuntu/release');
if ( isnull(os_release) ) audit(AUDIT_OS_NOT, 'Ubuntu');
os_release = chomp(os_release);
if (! ('18.04' >< os_release || '20.04' >< os_release || '22.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 18.04 / 20.04 / 22.04', 'Ubuntu ' + os_release);
if ( ! get_kb_item('Host/Debian/dpkg-l') ) audit(AUDIT_PACKAGE_LIST_MISSING);

var cpu = get_kb_item('Host/cpu');
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ('x86_64' >!< cpu && cpu !~ "^i[3-6]86$" && 's390' >!< cpu && 'aarch64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'Ubuntu', cpu);
var ubuntu_pro_detected = get_kb_item('Host/Ubuntu/Pro/Services/esm-apps');
ubuntu_pro_detected = !empty_or_null(ubuntu_pro_detected);

var pro_caveat_needed = FALSE;

var pkgs = [
    {'osver': '18.04', 'pkgname': 'dropbear', 'pkgver': '2017.75-3ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'dropbear-bin', 'pkgver': '2017.75-3ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'dropbear-initramfs', 'pkgver': '2017.75-3ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'dropbear-run', 'pkgver': '2017.75-3ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'dropbear', 'pkgver': '2019.78-2ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'dropbear-bin', 'pkgver': '2019.78-2ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'dropbear-initramfs', 'pkgver': '2019.78-2ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'dropbear-run', 'pkgver': '2019.78-2ubuntu0.1~esm1', 'ubuntu_pro': TRUE},
    {'osver': '22.04', 'pkgname': 'dropbear', 'pkgver': '2020.81-5ubuntu0.1', 'ubuntu_pro': FALSE},
    {'osver': '22.04', 'pkgname': 'dropbear-bin', 'pkgver': '2020.81-5ubuntu0.1', 'ubuntu_pro': FALSE},
    {'osver': '22.04', 'pkgname': 'dropbear-initramfs', 'pkgver': '2020.81-5ubuntu0.1', 'ubuntu_pro': FALSE},
    {'osver': '22.04', 'pkgname': 'dropbear-run', 'pkgver': '2020.81-5ubuntu0.1', 'ubuntu_pro': FALSE}
];

var flag = 0;
foreach var package_array ( pkgs ) {
  var osver = NULL;
  var pkgname = NULL;
  var pkgver = NULL;
  if (!empty_or_null(package_array['osver'])) osver = package_array['osver'];
  if (!empty_or_null(package_array['pkgname'])) pkgname = package_array['pkgname'];
  if (!empty_or_null(package_array['pkgver'])) pkgver = package_array['pkgver'];
  var pro_required = NULL;
  if (!empty_or_null(package_array['ubuntu_pro'])) pro_required = package_array['ubuntu_pro'];
  if (osver && pkgname && pkgver) {
    if (ubuntu_check(osver:osver, pkgname:pkgname, pkgver:pkgver)) {
        flag++;
        if (!ubuntu_pro_detected && !pro_caveat_needed) pro_caveat_needed = pro_required;
    }
  }
}

if (flag)
{
  var extra = '';
  if (pro_caveat_needed) {
    extra += 'NOTE: This vulnerability check contains fixes that apply to packages only \n';
    extra += 'available in Ubuntu ESM repositories. Access to these package security updates \n';
    extra += 'require an Ubuntu Pro subscription.\n\n';
  }
  extra += ubuntu_report_get();
  security_report_v4(
    port       : 0,
    severity   : SECURITY_HOLE,
    extra      : extra
  );
  exit(0);
}
else
{
  var tested = ubuntu_pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, 'dropbear / dropbear-bin / dropbear-initramfs / dropbear-run');
}