Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 26.04 LTS : YAML-LibYAML vulnerabilities (USN-8925-1)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-8925-1. 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(366021);
  script_version("1.2");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/10/15");

  script_cve_id("CVE-2017-20285", "CVE-2019-25777", "CVE-2026-63676");
  script_xref(name:"USN", value:"8925-1");

  script_name(english:"Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 26.04 LTS : YAML-LibYAML vulnerabilities (USN-8925-1)");

  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 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 26.04 LTS host has a package installed
that is affected by multiple vulnerabilities as referenced in the USN-8925-1 advisory.

    Dominique Dumont discovered that YAML-LibYAML did not correctly handle certain reflection operations. If a
    user or system were tricked into opening a specially crafted file, an attacker could possibly use this
    issue to delete files. This issue only affected Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. (CVE-2017-20285)

    It was discovered that YAML-LibYAML did not correctly handle parsing certain documents. If a user or
    automated system were tricked into opening a specially crafted file, an attacker could possibly use this
    issue to execute arbitrary code. This issue only affected Ubuntu 16.04 LTS and Ubuntu 18.04 LTS.
    (CVE-2019-25777)

    It was discovered that YAML-LibYAML contained a regular expression susceptible to catastrophic
    backtracking. If a user or automated system were tricked into opening a specially crafted file, an
    attacker could possibly use this issue to cause a denial of service. (CVE-2026-63676)

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-8925-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected libyaml-perl package.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2017-20285");

  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:"2026/09/14");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/10/14");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/10/15");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:16.04:-:lts");
  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:"cpe:/o:canonical:ubuntu_linux:24.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:26.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libyaml-perl");
  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) 2026 Canonical, Inc. / NASL script (C) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info2.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 || '22.04' >< os_release || '24.04' >< os_release || '26.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 16.04 / 18.04 / 20.04 / 22.04 / 24.04 / 26.04', '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': 'libyaml-perl', 'pkgver': '1.15-1ubuntu0.1~esm1', 'cves': ['CVE-2017-20285', 'CVE-2019-25777', 'CVE-2026-63676']},
    {'osver': '18.04', 'pkgname': 'libyaml-perl', 'pkgver': '1.24-1ubuntu0.1~esm1', 'cves': ['CVE-2017-20285', 'CVE-2019-25777', 'CVE-2026-63676']},
    {'osver': '20.04', 'pkgname': 'libyaml-perl', 'pkgver': '1.30-1ubuntu0.20.04.1~esm1', 'cves': ['CVE-2026-63676']},
    {'osver': '22.04', 'pkgname': 'libyaml-perl', 'pkgver': '1.30-1ubuntu0.22.04.1', 'cves': ['CVE-2026-63676']},
    {'osver': '24.04', 'pkgname': 'libyaml-perl', 'pkgver': '1.31-1ubuntu0.24.04.1', 'cves': ['CVE-2026-63676']},
    {'osver': '26.04', 'pkgname': 'libyaml-perl', 'pkgver': '1.31-1ubuntu0.26.04.1~esm1', 'cves': ['CVE-2026-63676']}
];

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'];
  if (!empty_or_null(package_array['cves'])) cves = package_array['cves'];
  if (osver && pkgname && pkgver) {
    if (deb_check(release:osver, prefix:pkgname, reference:pkgver, cves:cves)) flag++;
  }
}

if (flag)
{
  var extra = '';
  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, 'libyaml-perl');
}