Ubuntu 18.04 LTS / 20.04 LTS : Linux kernel vulnerabilities (USN-4576-1)

##
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-4576-1. The text
# itself is copyright (C) Canonical, Inc. See
# <http://www.ubuntu.com/usn/>. Ubuntu(R) is a registered
# trademark of Canonical, Inc.
##

include('compat.inc');

if (description)
{
  script_id(141451);
  script_version("1.7");
  script_set_attribute(attribute:"plugin_modification_date", value:"2024/01/09");

  script_cve_id(
    "CVE-2020-14314",
    "CVE-2020-14385",
    "CVE-2020-16119",
    "CVE-2020-16120",
    "CVE-2020-25285",
    "CVE-2020-25641"
  );
  script_xref(name:"USN", value:"4576-1");

  script_name(english:"Ubuntu 18.04 LTS / 20.04 LTS : Linux kernel vulnerabilities (USN-4576-1)");

  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 host has a package installed that is affected by multiple vulnerabilities as
referenced in the USN-4576-1 advisory.

  - A memory out-of-bounds read flaw was found in the Linux kernel before 5.9-rc2 with the ext3/ext4 file
    system, in the way it accesses a directory with broken indexing. This flaw allows a local user to crash
    the system if the directory exists. The highest threat from this vulnerability is to system availability.
    (CVE-2020-14314)

  - A flaw was found in the Linux kernel before 5.9-rc4. A failure of the file system metadata validator in
    XFS can cause an inode with a valid, user-creatable extended attribute to be flagged as corrupt. This can
    lead to the filesystem being shutdown, or otherwise rendered inaccessible until it is remounted, leading
    to a denial of service. The highest threat from this vulnerability is to system availability.
    (CVE-2020-14385)

  - Use-after-free vulnerability in the Linux kernel exploitable by a local attacker due to reuse of a DCCP
    socket with an attached dccps_hc_tx_ccid object as a listener after being released. Fixed in Ubuntu Linux
    kernel 5.4.0-51.56, 5.3.0-68.63, 4.15.0-121.123, 4.4.0-193.224, 3.13.0.182.191 and 3.2.0-149.196.
    (CVE-2020-16119)

  - Overlayfs did not properly perform permission checking when copying up files in an overlayfs and could be
    exploited from within a user namespace, if, for example, unprivileged user namespaces were allowed. It was
    possible to have a file not readable by an unprivileged user to be copied to a mountpoint controlled by
    the user, like a removable device. This was introduced in kernel version 4.19 by commit d1d04ef (ovl:
    stack file ops). This was fixed in kernel version 5.8 by commits 56230d9 (ovl: verify permissions in
    ovl_path_open()), 48bd024 (ovl: switch to mounter creds in readdir) and 05acefb (ovl: check permission
    to open real file). Additionally, commits 130fdbc (ovl: pass correct flags for opening real directory)
    and 292f902 (ovl: call secutiry hook in ovl_real_ioctl()) in kernel 5.8 might also be desired or
    necessary. These additional commits introduced a regression in overlay mounts within user namespaces which
    prevented access to files with ownership outside of the user namespace. This regression was mitigated by
    subsequent commit b6650da (ovl: do not fail because of O_NOATIMEi) in kernel 5.11. (CVE-2020-16120)

  - A race condition between hugetlb sysctl handlers in mm/hugetlb.c in the Linux kernel before 5.8.8 could be
    used by local attackers to corrupt memory, cause a NULL pointer dereference, or possibly have unspecified
    other impact, aka CID-17743798d812. (CVE-2020-25285)

  - A flaw was found in the Linux kernel's implementation of biovecs in versions before 5.9-rc7. A zero-length
    biovec request issued by the block subsystem could cause the kernel to enter an infinite loop, causing a
    denial of service. This flaw allows a local attacker with basic privileges to issue requests to a block
    device, resulting in a denial of service. The highest threat from this vulnerability is to system
    availability. (CVE-2020-25641)

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-4576-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected kernel package.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:N/C:P/I:P/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:U/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:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2020-16119");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");

  script_set_attribute(attribute:"vuln_publication_date", value:"2020/09/13");
  script_set_attribute(attribute:"patch_publication_date", value:"2020/10/14");
  script_set_attribute(attribute:"plugin_publication_date", value:"2020/10/14");

  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:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-1021-raspi");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-1026-kvm");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-1028-aws");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-1028-gcp");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-1028-oracle");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-1031-azure");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-51-generic");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-51-generic-lpae");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.4.0-51-lowlatency");
  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) 2020-2024 Canonical, Inc. / NASL script (C) 2020-2024 and is owned by Tenable, Inc. or an Affiliate thereof.");

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

  exit(0);
}

include('debian_package.inc');
include('ksplice.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)) audit(AUDIT_OS_NOT, 'Ubuntu 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 kernel_mappings = {
  '18.04': {
    '5.4.0': {
      'generic': '5.4.0-51',
      'generic-lpae': '5.4.0-51',
      'lowlatency': '5.4.0-51',
      'raspi': '5.4.0-1021',
      'aws': '5.4.0-1028',
      'gcp': '5.4.0-1028',
      'oracle': '5.4.0-1028',
      'azure': '5.4.0-1031'
    }
  },
  '20.04': {
    '5.4.0': {
      'generic': '5.4.0-51',
      'generic-lpae': '5.4.0-51',
      'lowlatency': '5.4.0-51',
      'raspi': '5.4.0-1021',
      'kvm': '5.4.0-1026',
      'aws': '5.4.0-1028',
      'gcp': '5.4.0-1028',
      'oracle': '5.4.0-1028',
      'azure': '5.4.0-1031'
    }
  }
};

var host_kernel_release = get_kb_item('Host/uptrack-uname-r');
if (empty_or_null(host_kernel_release)) host_kernel_release = get_kb_item_or_exit('Host/uname-r');
var host_kernel_base_version = get_kb_item_or_exit('Host/Debian/kernel-base-version');
var host_kernel_type = get_kb_item_or_exit('Host/Debian/kernel-type');
if(empty_or_null(kernel_mappings[os_release][host_kernel_base_version][host_kernel_type])) audit(AUDIT_INST_VER_NOT_VULN, 'kernel ' + host_kernel_release);

var extra = '';
var kernel_fixed_version = kernel_mappings[os_release][host_kernel_base_version][host_kernel_type] + "-" + host_kernel_type;
if (deb_ver_cmp(ver1:host_kernel_release, ver2:kernel_fixed_version) < 0)
{
  extra = extra + 'Running Kernel level of ' + host_kernel_release + ' does not meet the minimum fixed level of ' + kernel_fixed_version + ' for this advisory.\n\n';
}
  else
{
  audit(AUDIT_PATCH_INSTALLED, 'Kernel package for USN-4576-1');
}

if (get_one_kb_item('Host/ksplice/kernel-cves'))
{
  var cve_list = make_list('CVE-2020-14314', 'CVE-2020-14385', 'CVE-2020-16119', 'CVE-2020-16120', 'CVE-2020-25285', 'CVE-2020-25641');
  if (ksplice_cves_check(cve_list))
  {
    audit(AUDIT_PATCH_INSTALLED, 'KSplice hotfix for USN-4576-1');
  }
  else
  {
    extra = extra + ksplice_reporting_text();
  }
}
if (extra) {
  security_report_v4(
    port       : 0,
    severity   : SECURITY_WARNING,
    extra      : extra
  );
  exit(0);
}