Ubuntu 16.04 ESM / 18.04 LTS / 20.04 LTS : Bash vulnerability (USN-5380-1)

#%NASL_MIN_LEVEL 70300
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-5380-1. The text
# itself is copyright (C) Canonical, Inc. See
# <https://ubuntu.com/security/notices>. Ubuntu(R) is a registered
# trademark of Canonical, Inc.
##

include('deprecated_nasl_level.inc');
include('compat.inc');

if (description)
{
  script_id(159982);
  script_version("1.6");
  script_set_attribute(attribute:"plugin_modification_date", value:"2023/10/16");

  script_cve_id("CVE-2019-18276");
  script_xref(name:"USN", value:"5380-1");

  script_name(english:"Ubuntu 16.04 ESM / 18.04 LTS / 20.04 LTS : Bash vulnerability (USN-5380-1)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Ubuntu host is missing a security update.");
  script_set_attribute(attribute:"description", value:
"The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by a
vulnerability as referenced in the USN-5380-1 advisory.

  - An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default, if
    Bash is run with its effective UID not equal to its real UID, it will drop privileges by setting its
    effective UID to its real UID. However, it does so incorrectly. On Linux and other systems that support
    saved UID functionality, the saved UID is not dropped. An attacker with command execution in the shell
    can use enable -f for runtime loading of a new builtin, which can be a shared object that calls setuid()
    and therefore regains privileges. However, binaries running with an effective UID of 0 are unaffected.
    (CVE-2019-18276)

Note that Nessus has not tested for this issue 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-5380-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected bash, bash-builtins and / or bash-static packages.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:N/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:POC/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:P/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2019-18276");

  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:"2019/11/28");
  script_set_attribute(attribute:"patch_publication_date", value:"2022/04/20");
  script_set_attribute(attribute:"plugin_publication_date", value:"2022/04/20");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:16.04:-:esm");
  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:"p-cpe:/a:canonical:ubuntu_linux:bash");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:bash-builtins");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:bash-static");
  script_end_attributes();

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

  script_copyright(english:"Ubuntu Security Notice (C) 2022-2023 Canonical, Inc. / NASL script (C) 2022-2023 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info.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 (! ('16.04' >< os_release || '18.04' >< os_release || '20.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 16.04 / 18.04 / 20.04', '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 pkgs = [
    {'osver': '16.04', 'pkgname': 'bash', 'pkgver': '4.3-14ubuntu1.4+esm1'},
    {'osver': '16.04', 'pkgname': 'bash-builtins', 'pkgver': '4.3-14ubuntu1.4+esm1'},
    {'osver': '16.04', 'pkgname': 'bash-static', 'pkgver': '4.3-14ubuntu1.4+esm1'},
    {'osver': '18.04', 'pkgname': 'bash', 'pkgver': '4.4.18-2ubuntu1.3'},
    {'osver': '18.04', 'pkgname': 'bash-builtins', 'pkgver': '4.4.18-2ubuntu1.3'},
    {'osver': '18.04', 'pkgname': 'bash-static', 'pkgver': '4.4.18-2ubuntu1.3'},
    {'osver': '20.04', 'pkgname': 'bash', 'pkgver': '5.0-6ubuntu1.2'},
    {'osver': '20.04', 'pkgname': 'bash-builtins', 'pkgver': '5.0-6ubuntu1.2'},
    {'osver': '20.04', 'pkgname': 'bash-static', 'pkgver': '5.0-6ubuntu1.2'}
];

var flag = 0;
foreach 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'];
  if (osver && pkgname && pkgver) {
    if (ubuntu_check(osver:osver, pkgname:pkgname, pkgver:pkgver)) flag++;
  }
}

if (flag)
{
  security_report_v4(
    port       : 0,
    severity   : SECURITY_HOLE,
    extra      : ubuntu_report_get()
  );
  exit(0);
}
else
{
  var tested = ubuntu_pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, 'bash / bash-builtins / bash-static');
}